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LABORATORY NOTES 



ON THE 



STRENGTH OF MATERIALS 



BY 



MORTON O. WITHEY 

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Assistant Professor of Mechanics in The University of Wisconsin 



MADISON, WIS. 
UNIVERSITY CO-OPERATIVE COMPANY 
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Copyright, 1912, by Morton O. "Withey 



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CONTENTS 

Introduction 6 

Preliminary notes 7 

Class experiments 10 

1. Compression test of wood with wire-wound dial compresso- 

meter 10 

2. Tension test of mild steel with micrometer-screw extensometer . . 11 

3. Cross bending test of a wooden beam — loaded in middle — wire- 

wound dial deflectometer 12 

4. Impact test of cast iron on Russell impact machine 13 

5. Test of a small structural steel column 13 

6. Torsion test of steel 15 

7. Study of a universal lever testing machine and an hydraulic 

jack transverse testing machine 16 

Group experiments 16 

Test Si. Tensile tests of steels varying in carbon content 16 

Test S2. Extensometer tension test of high carbon steel and com- 
pression tests of steels 18 

Test S3. Various tests on wrought iron and steel 19 

Test S4. Effect of overstrain and subsequent annealing of steel — 
comparison of yield points and ultimate strengths of 

mild steel bars differing in size 20 

Test S5. Repeated stress tests on ferrous metals 20 

Test CI 1. Tensile tests of white, gray and malleable cast iron 21 

Test CI2. Extensomstsr ts.isioi t23t ail CDnprsssioi test of cast 

iron 22 

Test CI 3. Cross bending, impact, and torsion tests of cast iron. ... 22 

Test Wi. Tensile tests of aluminum and copper wires 23 

Test Ti. Cross bending and shear tests of different woods 23 

Test T2. Compression and impact tests of various woods 24 

Test T3. Cross bending tests of Norway pine, specimens differing 

in moisture content 25 

Test T4. The effect of the time clement on the cross bending 

strength of timber 2$ 

Test Bi. Tests of paving brick 26 

Test B2. Tests of building brick 26 

Tests made in the cement laboratory 27 

( /cneral instructions 27 

Test Cl. Tensile and compressive tests of mortars differing in 

richness of mixture 28 

Test C2. The standard commercial test of Portland cement 29 

Test C3. Compressive strengths of concrete cylinders of different 

proportions .>' 



Test C4. Cross bending test of a reinforced concrete beam 32 

Test C5. Tests for determining the quality of different sands 34 

Test C6j The effect of the fineness of cement upon the tensile 

strength of mortar 35 

Test C7, The effect of grading the size of sand grains upon the ten- 
sile strength of mortar 35 

Test C8. The standard commercial test of natural cement 36 

VI. A. S. T. M. Standard Specifications for Cement 36 

General observations 36 

Specifications 37 

VTI. Methods for testing cement recommended by the A. S. C. E. com- 
mittee 39 

Vm. Flexure formulas for reinforced concrete beams 50 

IX. The manufacture of pig and cast iron 54 

X. The manufacture of wrought iron and steel 62 

1. Methods of manufacture of wrought iron 62 

2. Methods of making steel 65 

XI. Limes and cements 75 

1 . Limes 75 

2. Natural cement 78 

3. Portland cement 79 

XII. Constants of strength for structural materials 89 



I. INTRODUCTION. 

In a large university in which laboratory instruction must be given by several 
teachers, it is quite necessary that some standard forms of notes be employed 
in order that every student may obtain identical instruction concerning the 
method of performing and reporting experiments. To be of greatest value, 
every student should be provided with a copy of such instructions. 

These notes are the outgrowth of several previous editions, the first of which 
was prepared by Professor H. F. Moore, of the University of Illinois. In the 
present edition more complete instructions relating to the methods of testing, 
new experiments, and notes on the manufacture of the ferrous metals and cements 
have been added. 

Obviously, this booklet in itself does not provide the student with adequate 
information concerning the mechanical properties of the materials tested. For 
this purpose numerous references to the leading texts, publications, and speci- 
fications have been given. Not only should these references be read in con- 
nection with the experiments, but, in a general way, a notion of the scope of 
each source of information should be obtained. Such an acquaintanceship with 
this field of technical literature will be of great value to the student if he should 
later desire further knowledge on kindred subjects. For purposes of discussing 
and fixing in mind the results of laboratory exercises, the important steps in the 
processes of manufacture, and the references it is also desirable to devote to 
recitations a portion of the time allotted for the course. At this university six 
or eight recitations per semester will be spent in this manner. 

The arrangement of the notes is such that during the first part of the course 
the class experiments will be performed, to a large extent, by the instructor. 
The purpose of these tests is to familiarize the student with the methods, ap- 
paratus, etc., used in the laboratory in making the common tests. An oppor- 
tunity is also afforded for the instructor to give assistance in methods of comput- 
ing and tabulating results, plotting curves, and explaining the purpose of the 
different tests. In the so-called group experiments the students will work in 
parties of two or three. The main object in these tests will be to study the me- 
chanical properties of materials themselves. 

Among the works consulted in preparation of this manual are: Johnson's 
Materials of Construction, Thurston's Materials of Engineering, Stoughton's 
The Metallurgy of Iron and Steel, Campbell's The Manufacture and Property s 
of Iron and Steel Howe's Iron, Steel and Other Alloys, Taylor and Thompson's 
Concrete Plain and Reinforced, Meade's Portland Cement, Taylor's Practical 
Cement Testing, Eckel's Cements, Limes and Plasters, Marten's Handbook of 
Testing Materials, The Journal of the Iron and Steel Institute, Proceedings of 
the American Society for Testing Materials and Tests of Metals (government 
reports). To these the student is also referred. 

I take pleasure in acknowledging the work of Professor Moore and tin- many 
suggestions received from members of the Mechanics' Department of this Uni- 
versity. Material for illustrations lias been kindly provided by Harbison-Walker 
Refractories Co. (Fig. 13, 14, 15, 17. 19. --. -7). Allis-Chalmers Co. (] 
30, 33), Illinois Steel Co. (Fig. 20, 2i, 23), Bradley Pulverizer Co. (Fig. ,;i 
Lehigh Car, Wheel and Axle Works (pig. 32), American Casting Machine Co* 
(Fig. 16), The American (May Machinery Co. (Fig. 35), Seaman-Sleeth C 
25), Engineering News (Fig. 34), Bradley Stoughton ' . W. P. Taylor 

(Fig. 28), P. Ilcroult (Fig. 24). 



7 Laboratory Notes 

II. PRELIMINARY NOTES. 

Read carefully before making each test. 

Note Book. — Every student should provide himself with a suitable labora- 
tory log-book in which all observations and test data should be recorded. A 
book 7x8^ inches having cross-section pages ruled with five divisions per linear 
inch is suggested for this purpose. This note book should be brought to every 
exercise in the course. To assist in forming an estimate of the grade of the stu- 
dent's work, the instructor will occasionally inspect the laboratory log-book. 

Examination of Specimen. — A critical examination of every specimen should 
be made and its previous history ascertained before the test is begun. The 
dimensions of all specimens should also be obtained as soon as they are received. 
Otherwise they may be broken before measurements are made and the test thus 
rendered worthless. 

Testing. — Before making the test the student should ascertain from the notes 
and instructor exactly what is to be done. He should carefully examine all in- 
struments and be certain that he understands how to operate or read them. 

Preliminary to placement of specimen in a lever testing machine, the weighing 
apparatus should be adjusted to balance with the beam reading zero and the recoil 
nuts "just loose." Also the knife edges should be examined to see that they rest 
upon their respective bearings. 

In a tensile test, the grips should never be placed as in Fig. ia or Fig. lb; 
but thin strips of metal, liners, should be used to secure a long grip parallel to 
the specimen, as in Fig. ic. This is very importaht. 

In a compression or cold bending test, the line of pressure in the specimen 
should coincide with the vertical axis of the machine. 




Fig.lc " 



FIG. I. — CORRECT AND INCORRECT 
METHODS OF GRIPPING TEN- 
SILE SPECIMENS. 



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Unit Deformation 

FIG. 2. TYPICAL STRESS-DEFORMATION 

CURVES. 



on the Strength of Materials 8 

If a spherical bearing block is employed in a compression test the student should 
be sure that the axis of the block, specimen, and machine are collinear. Unless 
the above condition obtains the benefit of the spherical seat is lost, and the spec- 
imen will be eccentrically loaded. 

When testing a ductile material or of an unknown material, the student should 
look for indications of the elastic limit. 

In all tests where apparatus for measuring deformations is employed, it is ad- 
visable to take more readings than are absolutely necessary rather than an insuffi- 
cient number. Superfluous readings may be discarded in computing results, but 
missing data can never be supplied after a specimen is broken. Deformation 
readings should always be taken while the beam on the testing machine is in 
balance. 

Although, to economize time in making a test, it is often desirable to use as 
fast a speed of the pulling head as possible; the beginner is urged to employ 
speeds less than one-eighth in. per min. until the elastic limit or yield point has 
been reached. After the elastic limit has been obtained a faster speed may be 
used in tension tests. In compression tests, however, it is better to employ 
a slow speed throughout the test. 

REPORTS 

Form. — Each report should be written in ink on regular laboratory paper 
form M3, and bound in a standard manila paper cover. Besides filling in the 
form on the outside of the cover, the student should also place upon it the names 
of his partners and instructor. 

In writing reports the student should pay due attention to the principles of 
grammar and composition. He should also strive to express his thoughts in as 
few words as possible. For each misspelled word a deduction of one per cent, 
will be made from the final mark given on the report. Lack of neatness or of 
clearness will be sufficient ground for rejecting a report. 

The following standard outline is suggested to assist in writing reports: — 

STANDARD OUTLINE FOR REPORTS 

1. Title. 

2. Object. 

3. Apparatus — sketches, description, etc. 

4. Method of performing experiment. 

5. Data — measurement of specimen, readings taken, etc. 

6. Computations — substitutions in formulae and tabulation of results. 

7. Curves. 

8. Conclusions. 

Title. — The title should indicate the subject of the experiment. In general 
the heading given an experiment in these notes will be sufficient. 

Object. — A concise statement of the purpose of the experiment should be 
made. 

Apparatus. — In most cases a lettered sketch of the apparatus drawn in ink, 
accompanied by a brief description referring to the letters on the sketch, will be 
a sufficient explanation of the device under consideration. Unless the student 
is very proficient in free hand perspective, he should. use a ruling pen and draw 
a plan and elevation of the object. 

Method. — Under this sub-heading a brief statement should be made tilling 
how the test was made. Whenever a similar method has been employed ir a 



9 Laboratory Notes 

previous report reference may be made to the same. New features in a test 
should, however, be described. 

Data. — Particular care should be taken to tabulate, in systematic form, all 
data taken during a test. Each student should take pains to check his data 
with that recorded by his partners before he leaves the laboratory, so that mis- 
takes arising from erroneous readings may be avoided. In many experiments 
printed blanks furnished by the laboratory may be used for tabulating the data 
and recording results of computations. 

Computations. — The computations employed in reducing data should be 
clearly indicated by one or more examples, and the numerical substitution in 
formulas from which the main results of the test are derived should always 
be given in full. 

Each report should contain a tabulated summary of results. Where a printed 
blank is given, this blank, properly filled out, will give such a summary, other- 
wise the student is to make his own tabulation. 

There is given at the end of these notes a table of average values of strength, 
moduli, etc., of various materials. This is given as a rough index of reliability 
of the student's work. Of course, the actual specimens tested will rarely, if ever ? 
have the exact properties given in the table ; but results differing greatly from these 
average values should not be passed in. In most cases such erratic results are 
due to mistakes in the figures or units in computation, more rarely they are due 
to to errors or mistakes in the test; in the latter case the test is to be repeated. 
All final results computed from test data should be accurate within one per cent. 

Curves. — For the sake of ease and uniformity, curves should be drawn on cross- 
section paper having either 10 or 20 divisions per linear inch, forms C3 or C2. 
A title should always be placed upon the curv T e sheet and the important results 
given a prominent position. In short, the curve sheet should contain the main 
information secured in the experiment. 

All curves should be inked, and the scales of the co-ordinates plainly stated. 
Curves should be drawn carefully with a curved ruler, and fine lines should be 
used. The points determining the curve should always be shown enclosed in 
a small circle. 

All load-deformation curves in this work should be smooth curves, not broken 
lines running from point to point. None of the materials tested give reversed 
curves of load and deformation. The student is especially cautioned to refrain 
from handing in "snaky" curves. The general form of load-deformation curves 
is shown in Fig. 2a for brittle materials, and in Fig. 2b for ductile materials. 

In nearly all tests involving measurement of load and deformation (elong- 
ation, compression, deflection, or twist) some initial load is put the on specimen to 
tighten up all parts before measuring deformation. When the load-deformation 
curve is plotted it appears as acb in Fig. 2b — not passing through zero but 
through c, oc being the initial load. 

In computing the modulus of elasticity, ob should be drawn parallel to acb and 
the modulus computed from ob. It is the slope of the load-deformation curve 
which is an index of the modulus of elasticity. 

Conclusion. — In general the conclusions should contain a brief summary of 
the important laws or results obtained from the test. The conclusions based upon 
the class tests, however, should also give the student's opinion of the accuracy and 
sensitiveness of the apparatus employed. The question of the suitability of the 
apparatus for the test considered should also be discussed. 



on the Strength of Materials io 

When reports are due. — Reports are due one week after the performing of a 
test; for each week or fraction of a week of tardiness in presenting the report, 
20 per cent, will be deducted from the grade, 60 per cent, being the maximum for 
tardiness, however. Students two weeks or more in arrears on reports cannot 
do work in the laboratory till arrears are made up. Laboratory exercises so lost 
will be acted upon by the department before permission to make up such arrears 
can be obtained. 

Reports returned for correction are due one week from the day they are re- 
turned, same penalty for tardiness as above. 



III. CLASS EXPERIMENTS. * 

1. Compression Test of Wood with Wire-Wound Dial Compressometer. 

Students should note the kind of specimen and determine its dimensions. 
The positions for the compressometer rings should next be marked with a gage 
length of six inches. Next the apparatus should be attached to the specimen 
so that the No. 36 covered copper wires leading to the dial are parallel to, equi- 
distant from, and in the same plane as the vertical gravity axis of the specimen. 
The smallest reading of the dial and the error in readings due to thickness of 
wire should be determined. Students should then inspect the apparatus and learn 
to read the dial. After the class has briefly examined the principle of operation 
of a testing machine, the specimen should be placed in the 100,000-lb. Riehle 
machine on a spherical bearing block and the pulling head of the machine lowered 
until it just touches the specimen which is held with its long axis vertical and coin- 
cident with that of the machine. The pointer on the dial should respond readily 
to a slight pressure against the wire. 

In general two or more students should read the dial during this test; the ma- 
chine should be handled by instructor. After taking the reading on dial cor- 
responding to no load on specimen the load should be applied in increments of 
500 lb. per sq. in. by hand, keeping the beam balanced while the dial is being read. 
Readings should not be taken until the dial pointer is approximately motionless. 
Students should note that there is no yield point well marked by a definite drop 
of the scale beam. The load should be applied for a short time after the specimen 
fails, to bring out the plane of rupture. Both specimen and compressometer 
should be taken to the recitation room. 

General directions regarding course, recitations and laboratory exercises, 
reference library, method of keeping laboratory notes, use of this manual 
before writing up experiments, reports, etc. will be given students in the recita- 
tion room. The method of filling out the standard form for reports will be 
carefully indicated. Particular attention should be paid to the object of the 
experiment and to sample sketches made of the apparatus. Forms for tabu- 
lating readings and computing unit stresses and unit deformations should be 
carefully noted. Convenient scales for ordinates and abscissae in this tost are 
r in. = 1,000 lb. per sq. in. and 1 in. = .001 in. per inch, respectively. Parti- 
rcula care should be taken to record the main results OD curve sheet. Rough 
computations of the results will often be made by instructor to aid the student 
in making his final computations. 



* Before making any test, all apparatus should be inspected to see that it 
is in working order. 



ii Laboratory Notes 

R esults wanted :- 

Unit stress at ultimate. 

Modulus of elasticity at a unit stress of 2000 lb. per sq. in. 
Energy of breaking per cu. in. 
Describe (with sketch) compressometer. 
Describe (with sketch) method of failure. 
References:- Johnson— Ch. Ill, Ch. XIII Par. 200, Ch. XVI Par. 278-282; 
Boyd — Art. 22, 29 and 32. 

2. Tension Test of Mild Steel with Micrometer-Screw Extensometer. 

Students should note the kind of specimen ascertain the reason for its shape 
and determine its dimensions. It should then be prick-punched over its entire 
gage length at points one inch apart. The electric-contact micrometer-screw 
extensometer with gage length of eight inches should next be placed on the speci- 
men and rigidly fastened in position by set screws. Students should note the 
necessity for having a full bearing surface for the micrometer screws on top of the 
posts. After placing the specimen in the grips of the testing machine, an initial 
load of 1,000 lb. should be applied to hold grips in place. The class should care- 
fully examine method of wiring to telephone receiver and battery, noting the part 
played by the gutta percha insulation in the cross arm at the foot of each post. 
When the least reading of the instrument has been found, a micrometer screw 
should be brought down until contact is made (only a horizontal pressure tan- 
gential to the circumference of the dials being used). Contact should be made 
and broken several times both to see that the electric current is of proper 
strength to operate the receiver and to test the sensitiveness of the extensometer. 
Then students sould inspect the apparatus thoroughly and make sketches. 

After two students have been appointed to read the extensometer, loads may 
be applied by hand in increments of approximately 5,000 lb. per sq. in. From 
time to time extensometer readings should be checked by determining the in- 
crement in the sum of the readings of the right and left dials. Within the elastic 
limit these increments should be equal if the increments of applied load are equal. 
Extensometer readings should not be taken until the specimen holds the beam 
balanced. When the elastic hmit is nearly reached the increments of loading 
should be cut down to 500 lb. per sq. in. The yield point may be determined by 
the drop of the beam and compared with the elastic limit observed by the increas- 
ing increments read on the extensometer. Extensometer readings should be 
taken until after the beam drops. After removing apparatus the specimen should 
be broken under a fast speed. When the yield point is passed the behavior of 
trie scale beam as the load is continually applied should be noted. Students 
should observe the load at which the specimen begins to neck down and note that 
the breaking load is less than this maximum load for mild steel, but they should 
record only the maximum load. (The breaking load is of no practical impor- 
tance, now, at least). Specimen and apparatus should be taken to recitation 
room. 

In the recitation room the standard form of test, as in class test 1, should be 
carefully considered. Particular attention should be paid to method of tabulat- 
ing data and reducing readings. Superfluous readings taken near the elastic limit 
may be omitted. The class should ascertain how to measure the reduced d «ameter 
and the increase in length in eight inches and in two inches. Students should 
find out the reason for the discrepancy in values of the percentage of elongation 
derived from these measurements. Scales to be used for coordinates of stress 



on the Strength of Materials 12 

elongation curve are: 1 in. =5000 lb. per sq. in. for ordinates and 1 in. =.0004 
inches per in. for abscissas. When the curve is plotted the zero correction to 
elongations should be shown. A rapid method of determining the modulus of 
elasticity is given in Fig. 2b. Particular attention should be given to the method 
of locating the elastic limit and yield point on the curve. The student should 
inform himself concerning the definition of elastic resilience, and he should be 
able to derive for it a simple expression in terms of the area under the stress-elong- 
ation curve. 

Results wanted :- 

Unit stress at elastic limit. 

Unit stress at yield point. 

Unit stress at ultimate. 

Modulus of elasticity. 

Elastic resilience per cu. in. 

Per cent, of elongation in eight inches. 

Per cent, of reduction in area. 

Sketch of extensometer used showing wiring circuit, battery, receiver 
specimen, etc. 

References:- J )hnson—Ch. II, Ch. XV Par. 264-274; Boyd — Art. 8-1 1, 15-22, 
24 and 32. 

3. Cross Bending Test of a Wooden Beam — Loaded in Middle — Wire-Wound 
Dial Deflectometer. 

Care should be taken to note the kind of specimen and to measure its cross- 
sec tional dimensions. The span should be also measured and vertical lines drawn 
on sides of the beam directly over the points where it is to be supported and 
below where it is to be loaded. The yoke with idler pulleys should be attached 
by brads driven into the beam at the middle. The side bars of the deflectometer 
can then be attached by nails driven into the beam over the supports at the neutral 
surface These bars should be held away from the specimen by means of washers 
slipped over the nails. The side bars should next be firmly clamped against the 
washers with a large iron clamp extending across top of beam. The dial and 
auxilliary pulley can then be attached to side bar. The portions of No. 36 covered 
copper wire leading from the side bars to yoke should be perpendicular to the 
bottom plane of the beam and equidistant from the sides. A fine distinct 
vertical line may be ruled on the side of the beam near the middle. The beam 
should then be placed on bearing plates surmounting the rocker supports of the 
transverse testing machine, and the whole apparatus inspected by students. 
Attention should be given to position of side bar supports, yoke supports, wires, 
dial, free end of side bars, rocker supports, wooden rocker at loading point, what 
the readings of the dial mean, and operation of testing machine. Next the scale 
beam should be balanced with test beam in place (wt. of test beam may be dis- 
regarded throughout), dial reading taken, and then the load applied in increments 
of 1000 lb. until beam fails. The load at first crack ami at failure and method 
of failure should be recorded. From time to time during the test a straight edge 
should be placed along the ruled line and the coincidence noted. 

In the class room students should be careful to find out what is wauled on the 

sketch. The definition of computed flexural strength (often called modulus 

of rupture) should be ascertained. In general, rough computations ^( all results 
will be made. Scales to be used for the load defied ion curve arc: ordinates 1 
in. =2000 lb., abscissa' 1 imo .2 in. 



13 Laboratory Xotes 

Results wanted :- 

Computed flexural strength or modulus of rupture. 
Modulus of elasticity at 2000 lb. per sq. in. on the extreme fiber. 
Energy of rupture per cu. in. 
References:- Johnson— Ch. V Par. 30, Ch. XVII; Boyd— Art. 55, 56 and 63. 

4. Impact Test of Cast Iron on Russell Impact Machine. 

After recording the dimensions of the specimen the method of operating the 
machine should be noted and the following determinations made: — 

1, — distance from axis to to center of percussion of pendulum, by the 

/n 

pendulum method — T = 2 w \ / g; 

2, — determination of the smallest reading of dial and vernier; 

3, — measurement of length of pendulum and distance from top to axis. 
Then the following adjustments may be made: — 

1 , — span ; 

2, — adjustment of pendulum to touch specimen when in vertical position 
(the vertical cap screws on top of axis bearings must be tight after this adjustment 
is made); 

3, — adjustment of specimen so that its center of gravity is opposite the 
center of percussion of pendulum; 

4, — adjustment of vernier zero to coincide with the zero on the dial. 

The stop acting on the vernier arm must not scrape against the dial after 
this adjustment is made. Care should also be taken to see that the screws back 
of the dial are tight. Xext a determination of the friction correction may be 
made. After raising pendulum to any desired height the vibration in the chain 
should be stopped before the dial is read. 

When the specimen has been placed in position the pendulum should be raised 
to an angle of approximately 20 degrees and the exact angle recorded. The 
pendulum ma}^ then be released and the angle to which it swings recorded. 

In recitation room the class should ascertain the unavoidable errors in the test, 
why the pendulum must strike the specimen at the center of percussion, and why 
impact testing does not give information concerning the resistance of a specimen 
to a static load. Students should make a sketch of the pendulum and derive 
an expression for the energy consumed in breaking a specimen. They should 
also pay careful attention to the use of the friction correction and to the computa- 
tion and tabulation of results. Five place values of natural cosines or versines 
should be used in making computations. 
Results wanted :- 

Energy of rupture per cu. in. 

Sketch of Russell impact machine — side elevation. 

References:- Johnson — Ch. XVIII to Par. 295, Ch. VI Par. 51 and 53. 



5. Test of a Small Structural Steel Column. 

(To be performed while class in mechanics is studying column theory). 

This test is to give the student an opportunity to study the strength and elastic 
properties of a built structural steel column. Students should inspect the speci- 
men, note the kind of material and the result of tensile tests made on it, the method 
of riveting, dimensions of component parts, etc. Each student should make 



on the Strength of Materials 14 

himself familiar with the operation of the 600,000-lb. hydraulic testing machine. 
The specimen should be placed on a cast iron bearing plate with its vertical axis 
coinciding with that of the machine. Another bearing block should be placed on 
top of the column and the piston head raised until weight of the upper compres- 
sion head is just supported by the column. (A man should be stationed at the 
oil pump, while it is running, to avoid any possibility of overloading the column). 
While the piston head is being raised four dial compressometer attachments with 
gage lengths of 50 inches may be fastened to the four outstanding legs of the angles, 
these compressometers should be placed so that neither the top nor bottom fix- 
tures are less than 1 X times the diameter of the column from the nearest end of 
the specimen, so that the wires on each attachment are equidistant from the 
sides of the outstanding leg to which it is attached and parallel to the axis of the 
column. Also, if there is sufficient time, four compressometer attachments should 
be placed near middle of column with gage lengths such that no rivet is included 
in the gage length. The same precautions should be observed in attaching com- 
pressometers as before. Students should see that all compressometers are in 
working order, and sketch the specimen and apparatus. Four students should 
be stationed in positions to read dials and one at the pump. Readings of dials 
should be taken with the weight of upper head (1000 lb.) resting on the column. 
The column may then be loaded in increments producing a stress of approximately 
3000 lb. per sq. in. and corresponding dial readings taken until it fails. (Dial 
readings should be taken until failure load is reached). Attention should be 
called to the load when scaling begins, when the column begins to buckle, and 
when it fails. Students should sketch column after failure. 

In the recitation room students should ascertain the equation for reducing 
pressure gage readings, and the reason for using compressometer attachments 
on each outstanding leg. If two sets of compressometer attachments were em- 
ployed, students should note carefully that the purpose of the second set was to 
measure the deformation in a solid section of leg of the column. Care should 
be taken to arrange a tabulation of readings and results, so that the unit deforma- 
tions for each leg of the column occupy adjacent divisions in the tabulation. 
Particular attention should also be given to the method of computing average 
unit deformations for each set of four compressometers. Any differences in re_ 
suits obtained by the two sets of apparatus should be noted and, if possible, ex- 
plained. Two stress-deformation curves should be drawn from which values 
for modulus of elasticity, based on average unit deformations obtained from the 
two sets of apparatus, should be computed. Values of the unit stress at the elastic 
limit, at the load at which column scaled, and at the ultimate should be computed 
and compared with values derived from tension tests of the material. Also the 
ultimate strength obtained in the test should be compared with values obtained 
from Rankine's and T. H. Johnson's formulae for mild steel columns with tint 
ends. 

Results wanted :- 

Values of modulus of elasticity. 

Ultimate strength. 

Elastic limit. 

Stress on column when it sealed. 

Effect of rivets mi stiffness of columns. 

Comparison of results of eolunin test with tensile tests on material. 

Ultimate strength figured from T. II. Johnson's and Rankine's I'ormul.e. 



15 Laboratory Notes 

Sketch of specimen and apparatus. 
Sketch of specimen at failure. 
References:- Johnson — Par. 284. and 365; Boyd — Ch. XIII. 

6. Torsion Test of Steel. 

(To be performed when the class in mechanics is taking torsion). 

The class will proceed to the Thurston machine and note carefully the method 
of operating it. how twist is transferred through specimen to the arm carrying 
the pendulum, propose of sine cam, pencil, drum etc. Students should then 
record the diameter of the drum and obtain the moment correction due to fric- 
tion. Next a piece of paper should be fastened to the drum: and, with pencil 
point well sharpened, the drum should be rotated, thus obtaining the zero line 
for the diagram. Students should clearly perceive the necessity for this line. 
In order to find the maximum twisting moment which the machine can exert, 
the pendulum arm should be raised to a horizontal position and supported by a 
vertical piece of wood resting on a scales. Care should be taken to see that the 
pencil traces a clear curve on the diagram as the pendulum is raised. The rela- 
tion between the maximum ordinate on the diagram and the moment exerted by 
the pendulum arm when in a horizontal position, should be clearly understood by 
all before the test is continued. After measuring the dimensions of a small steel 
torsion specimen it should be placed on the centering pivots and fastened firmly 
in jaws of machine with wedges. While wedging the specimen in the jaws the 
worm and gear should be disengaged. Students should inspect the apparatus 
and then proceed with the test. The following points should be carefully noted 
as the test proceeds; yield point, ultimate, detrusion of specimen at each point, 
kind of failure. The diagram should be preserved to be measured in recitation 
room. 

A test to determine the modulus of elasticity of a piece of 2 -inch cold-rolled 
steel shafting will be made, on the Riehle 1 25, ooo-in. lb. machine. Class should 
inspect power "end" and the method of weighing the twist applied to the speci- 
men. The operation of the torsion indicator should be carefully noted. Stud- 
ents should understand clearly that both dial and pointer move when the speci- 
men is twisted because they are mounted on disconnected axes and that the 
angles measured are those caused by the relative motion of the points of attach- 
ment of the arms. Students should caliper the specimen, measure the distance 
between the arms of the indicator, length of arms, diameter of sheaves, and 
determine how to read the dial. 

An initial load of 5,000 in. lb. should be applied to specimen and the indicator 
read. The specimen should then be loaded by hand in increments of 5,000 in. 
lb., up to 40, ceo in. lb. and corresponding indicator readings obtained. The 
load should then be "backed off" to 5,000 in, lb. and readings of the indicator 
noted as a check. Students should sketch the torsion indicator. 

In the recitation room students should make sure that they understand the 
object of each portion of the experiment. From the test performed on the 
Thurston machine, measurements of ordinates to the curve at the elastic limit 
and ultimate and measurements of [the abscissae at the ultimate should be made. 
Students should ascertain the definition of computed twisting strength, its use 
and make computations for the results required below. The class should pay 
particular attention to the tabulation and reduction of data obtained in the ex- 
periment on cold-rolled steel shafting. A curve should be plotted with detrusion 



on the Strength of Materials 16 

per unit of length in degrees as abscissae (i in. = .2 degrees) and twisting moment 
in in. lb. as ordinates (1 in. = 5,000 in. lb.). Students should bear in mind the 
necessity for making the zero correction to detrusions. 
Results wanted :- 

Unit stress at elastic limit. 

Computed twisting strength. 

Angle of twist at ultimate, in degrees. 

Shearing modulus of elasticity. 

Sketch of torsion indicator. 
References :-Johnson— Ch. IV and XIX; Boyd— Ch. XIV. 

7. Study of a Universal Lever Testing Machine and an Hydraulic Jack Trans- 
verse Testing Machine. 

First, the class should examine the 10,000-lb. Olsen (dismantled to show the 
lever system) and study the method of obtaining the "pound equivalent." Then 
the students should proceed to a Riehle' or Olsen machine and look over the weigh- 
ing system, lever system, poise, vernier on scale beam, recoil buffers etc. After 
the motor has been started, attention should be given to the method of trans- 
mitting power to the screws. Students should examine the control lever, speed 
changing levers, and the friction drive ; and they should carefully note what speeds 
should be used for ordinary tests. Attention should be given to the methods of 
using machines in tension, compression and cross-bending: the equipment of 
tools should be looked over and their uses ascertained. 

The class should next inspect the Johnson beam machine and study its opera- 
tion. Through the opened trap door in the floor, class should inspect the hy- 
draulic jack, the method of connecting the screws to the piston rod of the jack 
and the oil inlets. Attention should also be given to the weighing head, the 
method of raising and lowering the loading knife edge, the oil pump, and method 
of operating it. 

vStudents should then determine, in groups of two or three, the "pound equiva- 
lent" of the 10,000-lb. Olsen. Results will be checked by instructor before class 
is dismissed. Students should also make sketches of the side elevation of the uni- 
versal machine and of the side and end elevation of the Johnson beam-machine 
which will also be checked before they leave laboratory. 

Results wanted :- 

Diagrammatic sketch of the levers on the io,OD0-lb. Olsen universal machine. 

Pound equivalent for 10,000-lb. Olsen universal machine. 

Sketch and description of universal and transverse machines embodying the 
points taken up above. 

References:- Johnson — Par. 270 and 271. 



IV. GROUP EXPERIMENTS. 

Test S 1. Tensile Test of Steels Varying in Carbon Content. 

Before dividing the class into parties the instructor will perform a regular 
"commercial" test on a specimen of mild steel. Students should Irani how to 
measure a specimen with a micrometer and how to mark a specimen in a grooved 
holder with laying Off gage. Students Should appreciate the necessity for prick 
punching Specimen Over entire' length. The Specimen Should bo placed in .^rips 



17 Laboratory Notes 

(the usual caution being observed about the hold of the grips on the specimen) 
so that the length exposed between grips is not over four inches. The purpose 
and method of operating multiplying dividers should be carefully noted. After 
noting the reading of the dividers a load of eight-tenths of the estimated yield 
point should be applied on a medium speed. The divider reading should be noted 
again and the loading of specimen continued through the friction drive (slowest 
speed) until the yield point is reached. The class should then pay particular 
attention to scaling, drop of beam, change in rate of motion of divider arm, and 
should note the load at which this change takes place. Students should ascertain 
why the drop of beam does not always show the yield point accurately. The 
friction drive should then be released and, after a medium speed has been thrown 
in, the beam kept balanced until the specimen breaks. The poise should be left 
at the maximum load; the breaking load is of no practical value at the present 
time. Measurements should now be made of the reduction in area and the elonga- 
tion in 2 in. across break. The character of fracture (its geometrical shape and 
texture) should also be carefully observed. Much assistance in determining the 
texture of a fracture may be gotten from studying the broken ends of the nicked 
specimens kept in the apparatus room. 

Students should pay close attention to instructions in regard to inspection of 
machine, use of apparatus, tools, checks, dividing up work among individuals 
in a party and rotation in use of machines. 

Specimens. — Pieces of steel containing different percentages of carbon. Note 
per cent, of carbon and other ingredients. 

Apparatus. — Micrometer, punch, dividers, laying off gage, scale. 

Measurement of Specimen. — Micrometer and note the cross-section of specimen 
in three places. By means of gage and punch, lay off, marks I in. apart along 
the specimen. 

Test. — Make sure about the speeds by experimenting before gripping the 
specimen. As the load is applied, one man with the dividers set 2 in. apart 
should watch for signs of stretch in the specimen ; another should operate the ma- 
chine; and the third man should record, micrometer and measure specimens. 
Perform the test as outlined above. 

Report. — Fill out the blank furnished. Divide the cross-section paper into 
7-in. x 5-in. rectangles. Mark in one rectangle along 7 -in. side unit stresses at 
yield point and ultimate strength as ordinates (scales 1 in. = 20,000 lb. per sq. 
in.) ; in the other rectangle along 7-in. side per cent, of elongation in 2 in. and per 
cent, of reduction in area as ordinates (scale 1 in.= io per cent.) ; in both rectangles 
mark per cent, of carbon as abscissae (scale 1 in.=.2 per cent, carbon). Plot the 
individual results obtained in test and draw either broken or continuous straight 
lines through the average values, obtaining four curves with per cent, carbon as 
abscissae, and (a) unit stress at ultimate, (b) unit stress at yield point, (c) per cent, 
elongation in 2 in., (d) per cent, reduction of area as ordinates. State how (a), (b), 
(c), and (d) are affected by increasing the carbon content. Should steels (c) or 
(d) be used to make rails? (See A. S. T. M. Specifications for Steel Rails). 

The above is the ordinary "commercial" test of metals. 
References:- Johnson — Par. 356, 105-108, no- 129; Campbell — Page 368-372; 
Metcalf— Ch. IV.. 



on the Strength of Materials 18 

Test S 2. Extensometer Tension Test of High Carbon Steel and Compression 
Tests of Steel. 

(a) Extensometer Test. 

Specimen. — Piece of high carbon steel rod. 

Apparatus. — Micrometer-screw electric-contact extensometer reading to I- 10,000 
in., prick, punch, micrometer, laying-off gage, scale. 

Measurement of Specimen. — Micrometer the specimen at several places and 
note its diameter. Lay off prick punch marks 1 in. apart over the entire length 
of the specimen. 

Test. — Before performing this test read carefully the directions given in class 
experiment 2. Clamp the extensometer to the specimen and show to the in- 
structor before placing the specimen in the grips. After placing the specimen in 
the grips apply initial load of 3,000 lb.; then "back off" the load to 500 lb. by 
hand; take the zero readings of the extensometer. 

Apply the load slowly (by hand if machine has no very slow speed) and note 
the actual load and extensometer readings for increments of (approx.) =;ooo lb. 
per sq. in. up to (approx.) three-fourths of the estimated elastic limit. Be careful 
to distinguish between actual load and unit stress. Apply the load continuously, 
keeping beam balanced and stopping the application of load when the increment 
is added; if too much load is added for any increment, do not "back off," but 
read the load and corresponding extension. 

When a stress of three-fourths of the estimated elastic limit is reached, apply 
loads in increments of 1000 lb. per sq. in. until, by the behavior of the beam, you 
see that the yield point has been reached. 

When the yield point is reached record the load at which the beam dropped. 
Then take several readings, stretching the piece a little between the readings and 
note the corresponding loads at which the beam balances. 

Remove the extensometer, apply load continuously with a medium speed 
and break the specimen, noting the maximum load. 

Remove the specimen from the grips, measure across the break a length origin- 
ally 8 in. ; note the stretch, and micrometer and note the diameter of the reduced 

section. 

(b) Compression Test. 

Specimens. — Short cylindrical blocks of high carbon and mild steel. Record 
percentage of carbon in each specimen. 

Apparatus. — Compression blocks, micrometer, scale, chalk. 

Measurement of Specimens. — Length and diameter. 

Test. — Cover the outside of a specimen with chalk and place it between the 
compression tools, being careful to see that the axis of the specimen and a line 
through the center of gravity of the' pulling head of the machine coincide. Be- 
fore applying load ask instructor to inspect apparatus. Apply the load very 
slowly by hand keeping the beam balanced — get the yield point by observing 
when chalk begins to fall off the specimen and record the load. Continue apply- 
ing the load by the slowest power drive until 80 per cent, of the capacity of the 
machine is reached. Remove the specimen, sketch it.- appearance, and note 
the maximum load applied. 

Report. Make the description of each part a complete report in itself (follow 
through the standard outline in writing (a) and (b) but hand in the entire report 

in one cover sheet. 

(a) Extensometer Test. — Tabulate results as in elass test 2. 

Plot loads in pounds per sq. in. as ordinates (1 in. — 10,000 lb.) and ave. 
extensions per linear in. as abseiss:e (i in. = .0004 in.) 



x 9 Laboratory Xotes 

As in the class test and as directed in the introductory notes reduce this curve 
to zero co-ordinates, and find: 

Unit stress at elastic limit. 

Unit stress at yield point [drop of beamj. 

Unit stress at ultimate. 

Per cent, elongation in 8 inches and per cent, reduction of area. 

Modulus of elasticity. 

Place these results on curve sheet. 

Compare the modulus of elasticity with the value gotten in class test 2. 
(b) Compression Test. — Compute the unit stress at yield point. How does 
the unit stress at yield point in a compression test compare with the value ob- 
tained from a tension test of mild steel? For structural purposes what is the 
ultimate strength in compression of mild steel? How did the methods of failure 
of the mild and high carbon steels differ? Make sketches of each piece after 
test. What was the ultimate strength of the high carbon steel specimen? 
References:- Johnson — Par. 361-366, 36S, 18; Campbell — Page 337-392. 

Test S 3. Various Tests on Wrought Iron and Steel 

(a) Commercial Tensile Test of Wrought Iron. 

Make a tensile test of a piece of wrought iron, following the method of test 
Si. Compare its character of fracture with that of steel, noting the fibrous 
character of wrought iron. 

(b) Commercial Tensile Test of Boiler Plate Steel. 

Perform a commercial tensile test on a piece of boiler plate sheared to standard 
dimensions. 

(c) Shear Test. 

Specimen. — A flat bar cut from boiler plate used in (b). 

Apparatus. — Shearing tools, micrometer, scale. 

Measurement of Specimen. — Measure the dimensions of cross-section. 

Test. — Put the specimen in the shear tool so that the portion of the specimen 
to be sheared off is in the center of the tool and rigidly held by the clamping 
screws. This is necessary in order to avoid bending the specimen. Xote the 
number of surfaces over which a shearing stress is produced. Place the apparatus 
in the testing machine and apply the load by hand until the specimen breaks. 
Record failure load and character of fracture. 

(d) Cold Bending Test. 
Specimens. — Flat pieces of iron or steel. 
Measurement of Specimen. — Size of cross-section. 

Test. — Employ a four-screw testing machine in this experiment. Bend the 
specimen into V shape on cross bending tools, then place it between compression 
tools and close the V down flat or until crack appears. Be careful not to over- 
load the machine. Xote the approximate angle between the legs of the V when 
the crack appears. Sketch the piece after the test. This is a rough shop test 
to determine the ductility and toughness of a specimen. 

Report. — Make the description of each part a complete report in itself but 
hand in the entire report in one cover sheet. 

(a) Tensile Test of Wrought Iron . — Fill out the standard blank, comparing 
the fracture with steel. How does the ultimate strength of wrought iron compare 
with that of steel? Determine the grade of this iron from the Standard Speci- 
fications for Wrought Iron adopted by the A. S. T. M. 

(b) Tensile Test of Boiler Plate. — Put the results on the standard blank used 



on the Strength of Materials 20 

in (a). Determine the grade of boilerplate from the Standird Specifications for 
Open-Hearth Boiler Plate and Rivet Steel adopted by the A. S. T. M. 

(c) Shear Test. — Compute the average unit shearing stress at rupture. Com- 
pute the ratio of the average ultimate unit stress in tension (from test b) to the 
average ultimate unit stress in shear. Make a front and side elevation of the 
shear tool with a specimen in place. 

(d) Cold Bending Test. — State the size of the piece, angle to which it was bent 
before the first crack appeared, and give a sketch of the piece after test. 

References:- Johnson — Ch. XIX and XX, Par. 356-360, 372, 374. 

Test S 4. Effect of Overstrain and Subsequent Annealing of Steel — Com- 
parison of Yield Points and Ultimate Strengths of Mild Steel Bars Differing in 

Size. 

Specimens. — Pieces of mild steel. 

Apparatus. — Micrometer, punch, multiplying dividers, laying off gage and 
scale. 

Measurement of Specimen.— Micrometer the cross-section and note size. 

Test. — Perform the ordinary commercial test on one specimen of each size. 
Stress a second specimen of each size up to the yield point. Record this load and 
continue loading the specimen up to nine-tenths the maximum load of the sim- 
ilar specimen of the first set tested. Release the load, mark the specimen so that 
it can be identified and hand to the instructor, to be annealed. After the specimen 
is annealed perform the regular commercial test, making a new measurement of 
its diameter and placing punch marks over its entire length 1 in. apart. Load 
the remaining specimens up to nine-tenths the maximum load of the first set 
tested, noting the yield point, and release the load. Again apply load to the 
specimen until it breaks, being careful to note the new yield point. Measure 
the reduced diameter and the elongation in 2 in. 

Report.— Compute unit stresses at all yield points, at nine-tenths of the maxi- 
mum load, and at the maximum load. Also compute per cent, of elongation 
in 2 in. and per cent, of reduction in area. Tabulate results on the standard 
tensile test blanks, putting specimens of the same size on a sheet. Draw up a 
table containing columns headed size of bar, average normal yield point, 
and average normal ultimate strength. Draw up a second table containing 
columns headed size of rod, average normal yield point, yield point after anneal- 
ing, average normal percent, of reduction in area, percent, of reduction in area 
after annealing, normal per cent, of elongation in 2 inches and percent, of elonga- 
tion in 2 inches after annealing. In general, how does the size of cross-section 
of a mild steel rod affect its yield point and ultimate strength? TTow arc the 
yield point and ultimate strength affected by stressing mild steel beyond the yield 
point? What is the effect on the yield point, ultimate-strength, per cent, of 
elongation and reduction in area of heating an over-stressed mild steel bar to a 
temperature of °P. and allowing it to cool in ? Does the 

temperature and rapidity of cooling affect the properties of overstressed bars 5 

References:- Johnson — Par. 130-13411, 367, 370, 373, 395-400; Metcalf -Page 
68-76; Campbell -Page 274 — 285. 

Test S 5. Repeated Stress Tests on Ferrous Metals. 

Specimens. Two, |-in. round rods 8 in. long of each <'( the following metals: 
gray iron, malleable iron, wrought iron, mild steel, high carbon steel, and vana- 
dium steel. 



21 Laboratory Xotes 

Apparatus. — Landgraf-Turner imp act -bending testing machine, micrometer, 
and scale. 

Measurement of Specimens. — Micrometer the diameters of specimens and 
record results. 

Test. — Ascertain from the results of tension tests the yield point, ultimate 
strength, percentage of elongation, and percentage of reduction in area for each 
kind of specimen. Also secure the chemical composition of the various metals. 

In accordance with tne directions of the instructor, make the width of the slot 
on the Landgraf-Turner machine t3, in. and arrange the cams on the shaft so 
that a specimen will be deflected f in. Slip a specimen through the slot and 
clamp it rigidly in the jaws of the macnine. See that the size of the pulley on 
the motor is such that 300 "cycles of stress" will be given to the specimen per min 
Start the motor and throw in the clutch on machine Note the number of cycles 
when the specimen breaks. 

Report. — Tabulate the tensile test results and the number of "cycles of stress" 
at failure on a standard blank. Discuss the resistance of the different metals to 
repeated stresses. Could the relative resistance of these metals to such stresses 
be predicted from any of the results obtained in the tensile tests? 

References:- Johnson — Par. 383-386; Engimsring — April 24 and May 1 
1908. 



Test CI 1. Tensile Test of White, Gray and Malleable Cast Iron. 

The instructor may perform before the class a test on pieces of malleable iron 
with the outside shell removed. 

Specimens. — Tension test pieces of white, gray and malleable cast iron. 

Apparatus. — Micrometer, prick, punch, seale, multiplying dividers. 

Measurement of Specimen. — Micrometer at several p Dints, recording diameter. 
Prick-punch marks 1 in. apart over entire length of specimen. 

Test. — Xote the bright metallic ring of the white, the dull ring of the malleable, 
and the "dead" sound of the grey iron when the specimens are dropped on the 
cement floor. Place a specimen in the grips and apply the load slowly, keeping 
the beam balanced until the piece breaks. Watch carefully to see if there is any 
"drop" of beam or any indication of yield point by the dividers. Xote the load 
at yield point, if it occurs, and the load at ultimate. Xote whether the maximum 
and the breaking loads come together. 

Remove the specimen after rupture and see if there is any permanent elonga- 
tion or reduction of area and if so, note. Examine closely the character of fracture 
and record. 

Report. — Follow the usual method for a commercial test with a regular printed 
blank. Xote the appearance and color of fractured surface carefully. If the 
test is made on a specimen of malleable iron with skin turned off, make a regular 
tabulation of the results and compute the ratio of strength of the interior portion 
to the strength of the skin. How does malleable iron differ from white iron in 
strength, ductility, and hardness? 

References :-Johnson — Par. 61-68, 80-82, 106, 347-349; Keep — Ch. IV, 
Page 131-140. 



on the Strength of Materials 22 

Test CI 2. Extensometer Tension Test and Compression Test of Cast Iron. 
Specimens. — Long tensile test piece and short comp. test piece of cast iron (gray). 
Apparatus. — Extensometer, micrometer, scale, laying off gage, punch, steel ring. 

(a) Tensile Test. 

Measurement of Specimen. — Micrometer at several points and note the di- 
ameter. 

Test. — Attach the extensometer-points 8 in. apart, place the specimen in the 
grips and call the instructor to inspect the apparatus. Apply the load by hand 
in increments of 1,000 lb., up to 12,000 lb. Read and note loads and correspond- 
ing extensometer readings. 

At 12,000 lb., remove the extensometer; then apply the load till the piece 
breaks, keeping beam balanced. Note the breaking load and character of fracture . 

(b) Compression Test. 

Measurement of Specimen. — Micrometer the diameter and record. Also 
note the length. 

Test. — Place the compression blocks in the center of the machine and put the 
specimen in the center of the blocks with a ring around it to catch flying pieces- 
Very slowly apply load. Note the angle that the plane of rupture makes with the 
base of the specimen and draw a sketch. 

Report. — 

(a) Tensile Test. Tabulate data as in class test 2. Plot loads per sq. in 
and elongation per inch. Use as scales, 1 in. = 2,000 lb. per sq. in. and 1 in. 
=.0004 in. per in. (abscissae on short side of paper). Find the modulus of 
elasticity at unit stress of 5,000 lb. per sq. in., modulus of elasticity at unit stress 
of 10,000 lb. per sq. in., and unit tensile stress at ultimate. Record these results 
on curve sheet. 

(b) Compression Test. Find the unit compressive stress at ultimate and the 
ratio of the compressive to the tensile strength. Sketch compression fracture. 

References : -Johnson — Par. 79 and 350. 



Test CI 3. Cross Bending. Impact and Torsion Tests of Cast Iron. 

Specimens. — One gray iron, one white iron and one malleable iron bar for the 
cross bending test and a like number for the impact test, one torsion specimen o 
gray cast iron. 

Apparatus. — Cross bending tools, scales, deflectometer, torsion machine , 
impact machine, micrometer, wrenches, wedges for torsion machine. 

(a) Cross Bending Test. 

Measurement of Specimen. — Measure the cross-section and note the dimen- 
sions. Place the specimen over a 12-in. span with loading knife edge anu deflect- 
ometer at middle. 

Test. — Apply the load in increments, giving a deflection of .02 in. up to rupture, 
keeping the beam as nearly balanced as possible. Note loads and deflections. 

(b) Impact Test. 

Adjust machine as in class test and make span 12 in. 

Measurement of Specimen. -Measure the cross-section and note dimensions. 
Test.— Using the initial angles given on the card at impact machine, break 
the specimens. Note carefully both initial and final angles. 

(c) Torsion Test. 

Measurement of Specimen. - Micrometer the diameter and measure 1 he Length 

bel ween shoulders. 



2 3 Laboratory Notes 

Test. — Place the specimen in the machine and put paper on the drum as in 
class test 6. When this is done have the instructor inspect apparatus. After 
inspection of apparatus break the specimen, keeping the diagram for reference 

Report. — Describe each part separately but bind in one cover sheet. Be 
careful to indicate fully all computations. 

(a) Cross Bending Test. — Plot load-deflection curves for each specimen; 
use as scales I in. = 200 lb. and 1 in. = .04 in. (abscissas on short side of paper). 

From these curves get the modulus of elasticity for a point at which the maxi- 
mum unit fiber stress is 10,000 lb. per sq. in. Also, from the area under the curves 
(gotten by planimeter or by averaging ordinates) find the work done percu.in. 
in rupturing specimens. Make computations for the computed flexural strength 
(modulus of rupture) . Place these results on the curve sheet in order of magnitude . 

(b) Impact Test. — Compute the work per cu. in. required to rupture each 
specimen by impact and compare with the work per cu. in. found in the cross bend- 
ing test. Compare the resistances to shock of the three grades of iron. 

(c) Torsion Test. — Make a computation for the computed twisting strength 
(modulus of torsion) of gray .cast iron and sketch the fracture. Hand in the dia- 
gram obtained from machine. 

References : -Johnson — Par. 78, 291-294, 349. 

Test W 1. Tensile Tests of Aluminum and Copper Wires. 

Specimens. — Pieces of Aluminum and Copper wires. 

Apparatus. — Dial extensometer with special wire attachments, laying off gage, 
punch, micrometer, scale. 

Measurement of Specimen. — Micrometer the diameter at several points and 
note. 

Test. — Place ink marks 1 in. apart over the entire length of the specimen* 
Read the method of attaching extensometer given in class test 5. Place the at- 
tachments on the wire 8 in. apart and fasten the extensometer to them. Make 
the test in either a 10,000-lb. or a 20,000-lb. Olsen machine, using special grips. 
Have the instructor inspect the apparatus before applying load. Load with 
increments of approximately 1,000 lb. per sq. in. for aluminum or copper. Note 
loads and extensometer readings until the specimen ruptures. ■ Measure the diam- 
eters of broken pieces; break them again, noting load at yield point and ultimate. 

Report.— Tabulate and reduce representative readings from those taken on 
each specimen, being careful to pick 6 or 8 below the yield point. Plot stress- 
deformation curves and make computations as in test S 2. Employ as scales, 
1 in. = 4,000 lb. per sq. in. — ordinates — and 1 in. = .0004 in. per in. — abscissae. 

Compare the unit stress in the original piece at yield point and ultimate with 
similar properties of- the fragments. The purpose of this comparison is to show 
the effect of cold drawing on strength of wire. Compute the modulus of elas- 
ticity at a stress of 3,000 lb. per sq. in., percentage of elongation in 8 in., and the 
percentage of reduction in area. 

References :-Johnson—Ch. XXVIII and XXXIII. 

Test T 1. Cross Bending and Shear Tests of Different Woods. 

(a) Cross Bending Test. 

Specimens. — One or more small beams of each of the various woods. 
Apparatus. — Cross bending tools, scale, deflect ometer. 
Measurement of Specimens. — Cross-section and length of span. 



ON THE STRENGTH OF MATERIALS 24 

Test. — Place a specimen on the supports and load it at the center. Arrange 
deflectometer under load. Small flat pieces of steel should be placed on top of 
the supports and under the center knife edge to prevent cutting of the fibsrs of 
the specimen. Apply load in increments giving .02 in. deflection. Note 
loads and corresponding deflections. This test may well be performed in an 
autographic transverse testing machine. 

(b) Shear Test (with grain). 

Specimens. — Two shearing blocks of each of the various woods. 

Apparatus. — Shear tool, scale. 

Measurement of Specimens. — Cross-section of the projecting shoulder should 
be determined. 

Test. — Place a specimen in the shear tool as shown by the instructor, apply 
load slowly by hand and keep the beam balanced. Note the load when the piece 
shears. 

Report. — Make the report on each part of this experiment complete in itself 
but bind both in one cover sheet: 

(a) Cross Bending Test. — Find the computed flexural strength (modulus of 
rupture) of each kind of timber and tabulate the woods in order of the magnitude 
of the moduli of rupture. Also from this test plot load-deflection curves for each 
specimen: compute moduli of elasticity at a load of 403 lb. for all wools, and tabu- 
late according to stiffness. Use the following scales: 1 in. = 200 lb. — ordi- 
nates — and 1 in. = .04 in. — abscissae. 

(b) Shear Test. — Compute the ultimate unit longitudinal shearing stress of 
each wood and tabulate these values in order of magnitude of stress. Draw a 
sketch of the shear tool. 

References : -Johnson — Par. 178-182, 189-191, 197-199,201, 339, 312,442, 
and 443. 

Test T 2. Compression and Impact Tests of Various Woods. 

(a) Compression Test. 

Specimens. — Compression blocks of various woods. 

Apparatus. — Compression tools, scale, dividers. 

Measurement of Specimen. — Cross-section and length. 

Test. — (1) With grain: crush one specimen of each kind, applying load 
slowly ; note the load when a specimen fails. 

(2) Across grain: crush one specimen of each kind noting the load when a 
specimen has been compressed 15 percent, of its original height, measured by 
dividers set to 85 percent, of its original height. (This is a test for comparative 
purposes only). Determine the weight per cu. ft. of each wood. 

(b) Impact Test. 

Specimens. — One or more small beams of each of the various woods. 

Apparatus. — Impact machine, scale. 

Measurement of Specimen. — Cross-section. 

Adjustments of Machine.— Measurement of friction, adjustment oi specimen 
to center of percussion, adjustment of pendulum to specimen. Use 12-in. span 
unless otherwise Specified. 

Test.— Break the specimens, using initial angles posted near the machine* 

Use the same initial angle for as many specimens as possible and save computa- 
tion in the report . 
Report. Make the report on each part of this experiment complete in itseU 



2 5 Laboratory Xotes 

but bind both in one cover sheet. 

(a) Compression Test. — Compute the ultimate unit compressive stresses of 
woods with and across grain, and tabulate woods in order of their strength. 
Compare the strengths developed by crushing with the grain with those obtained 
across the grain. Plot a curve with ultimate strengths as ordinates and weights 
per cu. ft. as abscissa;. Scales : — I in. =2000 lb. per sq. in. and 1 in. =5 lb. per cu. ft. 

(b) Impact Test. Compute the energy per cu. in. required to break pieces 
and tabulate woods according to toughness. How does the energy of rupture 
of woods compare with that of cast iron [see CI3 (b)]? 

References :-Johnson — Par. 200, 206, 343, 344, 442, 443. 

Test T 3. Cross Bending Tests of Norway Pine Specimens Differing in Moisture 
Content. 

Specimens. — Wet and dry pieces of pine from the same stick, one piece soaked, 
one wet, and one dry. 

Apparatus. — Cross bending tools, scale deflectometer. 

Measurement of Specimen. — Cross-section and length of span. 

Test. — Weigh each specimen and compute the percentage of moisture in each 
by comparing with weight of specimen dried to constant weight. Perform a 
cross bending test to rupture; apply loads in increments giving .02 in. deflection; 
note loads and deflections. Observe the precautions given in T 1 in supporting 
a specimen. 

Report. — Compute the transverse strengths (moduli of rupture) ; also calculate 
the moduli of elasticity at a load of 400 lb., plotting load-deflection curves. Use 
the same scales as in T 1. 

Also plot a curve showing variation in modulus of rupture and modulus of 
elasticity with percentage of moisture. Select your own scales. 

Compare the strengths and the stiffnesses of corresponding wet and dry sticks. 

References:- Johnson — Par. 202, 441, 442. 

Test T 4. The Effect of the Time Element on the Cross Bending strength of 
Timber. 

Specimens. — One or more straight-grained strips of yellow pine. 

Apparatus. — Scale, 14-quart pail, 50 lb. of sand, and special I-beam-lever 
transverse testing apparatus. 

Measurement of Specimen. — Determine the depth and breadth, and cut the 
specimen into two portions of equal length. 

Test. — Arrange one portion of the specimen in apparatus with greatest cross- 
sectional dimension vertical. Place the supports two feet apart and load at the 
center. Hang the pail on the end of the I-beam and very slowly fill with sand 
until the specimen breaks. Record the weight of sand and pail. Determine 
the load on a specimen due to the weight of I-beam lever and compute the ratio 
of the lever arms. 

Calculate the necessary load which should be placed on the end of the I-beam 
to produce a center load on a beam equal to 85 per cent, of the above breaking 
load. Place remainder of the original specimen in the apparatus and leave the 
computed load upon it. Ascertain from the laboratory assistant the approxi- 
mate time of failure of this specimen. 

Report. — Describe the experiment, compute the modulus of rupture for each 
portion of the specimen, and state conclusions regarding the effect of the time 
element on the cross bending strength of yellow pine. 



on the Strength of Materials 26 

References:- Johnson — Par. 346b; Proc. A. S. T. M. 1909 — Page 534. 

Test B 1. Tests of Paving Brick. 

Specimens. — Twelve paving brick of the block type. 

Apparatus. — Machine for cross bending, cross bending tools with spherical 
bearings, scale, and rattler. 

Cross Bending Test. — Measure two brick, place on edge on the cross bending 
tools and determine the breaking load at the middle of the span. 

Rattler Test. — Weigh ten brick, which have been previously dried at least three 
hours in a temperature of 212 F., and place them in the rattler toegther with 

10 cast iron spheres 2>H in- i n diameter and a sufficient number of smaller spheres 

1 1 in. in diameter to make the total charge of spheres weigh 300 lb. After 
the rattler has made 1,800 revolutions at a speed between 29^2 and 30^ 
r. p. m. stop the test and again weigh the brick. Pieces weighing less than one 
pound should be discarded in the final weighing. Consult the Specifications for 
the Standard Rattler Test for the Paving Brick adopted by the N. P. B. M. 
A. in 191 1 and ascertain the restrictions placed upon the abrasive charge, 
upon the brick charge, and upon the method of operating the rattler. Also note 
standard form adopted for report. 

Absorption Test. — Take two or more bricks which have been submitted to 
the rattler test and place them in an oven. Dry the brick to constant weight and 
then place in water for 48 hours. Dry the surfaces with blotting paper and weigh 
again. Weighing should be done on scales sensitive and accurate to 0.01 pound. 
The increase in weight divided by the dry weight and multiplied by 100 gives 
the percentage of absorption. 

Specific Gravity. — Determine the weight in water of the brick used in the ab- 
sorption test after they have been immersed 48 hours. The dry weight divided 
by the difference between the wet weight and the weight in water after soaking 
gives the specific gravity. (Pore spaces are included in this computation). 

Report. — State the method of performing each portion of the test. Fill out 
the blank provided for this test. 

Good paving brick should not lose more than 25 per cent, by weight in the rattler 
test. An increase in weight of more than 3 per cent, or less than 1 percent, in the 
absorption test is not allowable. In the cross bending test the modulus of rup- 
ture should be at least 2000 lb. per sq. in. Would the brick tested be suitable for 
a first class pavement? 

References:- Baker's Roads and Pavements — Page 462-487; Proc. A. S. 
T. M. 191 1— Page 776; Johnson — Ch. XII. 

Test B 2. Tests of Building Brick. 

Specimens. — Three common clay, three sand lime, and three pressed brick. 

Apparatus. — Machine for crushing and cross bending, scale, blotting paper. 

Cross Bending. — After measuring the specimens, break two common clay, two 
pressed brick and two sand lime brick flatwise over a 7-in. Span. Record the 
breaking loads. 

Crushing Test. -Measure one broken half of each brick. Crush these pieces 
flatwise, using spherical tools and blotting paper between the tools and surfaces 
of the brick'. Record the crushing loads. After making the absorption test 
crush the half brick used, while still wet, and note the breaking loads. 

Absorption Test. See test B 1. 



27 Laboratory Notes 

Specific Gravity. — See test B i. 

Report. — State the method, of carrying on each test. 

Tabulate moduli of rupture for all cross binding tests, crushing strength wet, 
crushing strength dry, percentage of absorption, and. specific gravity. 

State your opinion of the brick tested after reading the specifications proposed 
by the A. S. T. M. (see Proc. A. S. T. Af. 1909— Page 131.) 

References :-Baker's Masonry Construction — Ch. II. 

V. TESTS MADE IN THE CEMENT LABORATORY. 

General Instructions for Work in the Cement Laboratory. 

Purpose of Course. — The purpose of this course is to give the student a general 
idea of some of the physical properties of cement and concrete and the various 
methods of testing them. It is not expected that a student will be an expert 
cement tester when he finishes these exercises, but it is hoped that he will have 
mastered the main principles of operation sufficiently to be able to perform care- 
fully the ordinary tensile or compressive tests. The correct interpretation of the 
results obtained can only come after considerable experience. It is only by close 
observations of rides and specifications, however, that even this may be accom- 
plished. 

Apparatus. — Each student will be assigned a section at one of the laboratory 
tables and a set of apparatus for which he will be held responsible. Apparatus 
other than that provided at his section ma}' be obtained from the instructor when 
it is needed. All apparatus, tools, etc., must be cleaned immediately after using. 
Tables and testing machines must be kept free from litter and broken briquettes. 
Such refuse material, as fast as it accrues, should be thrown into the galvanized 
iron buckets furnished for this purpose. Do not throw it on the floor. Neatness 
is one of the necessary requirements for the successful operation of a cement labo- 
ratory. 

Sampling Materials. — Since the quality of a considerable amount of material 
must frequently be judged from the results of tests made on a very small sample, 
it is of prime importance that such a sample truly represents the whole. The 
method of sampling cement is indicated on page 39 : other materials may be sampled 
as follows: 

Secure from different portions of the pile or bank a sufficient number of repre- 
sentative samples of equal size to provide, when mixed together, 5 or 6 cu. ft. of 
the material. Thoroughly mix the sample in a dry concrete mixer, or by the 
method of hand mixing employed in concrete work, turning the material at least 
20 times. Spread the material in a flat pile of circular plan, and cut out a quad- 
rant. Spread the quardant in a smaller flat circular pile and subdivide it in the 
same way, continuing the so-called method of quartering until a quadrant of 
material of the size desired for a sample is obtained. Employ this method when- 
ever necessary in the tests which follow. 

Making Specimens. — As far as possible, in all tests, follow the methods of mix- 
ing and molding given in the A. S. C. E. Methods for Jesting Cement (see pages 
45-47). Preliminary' to making the first test the instructor will illustrate the 
methods of cleaning and oiling the molds, and will show how briquettes should be 
made. 

In making briquettes and cubes the student should exercise great care to see that 
the molds are properly oiled and clamped together in such a manner that the 
specimens will be perfectly symmetrical. Leave the bottom boards and gal- 



on the Strength of Materials 28 

vanized iron strips under the specimens when they are placed in the moist closet. 

Record in the note book the date at which specimens should be tested. 

Marking Specimens. — ivvery specimen should be so marked that the student 
can tell when and how it was made, and of what materials it consists. Such 
marks should always be made on the end portions of the briquettes. Tests of 
specimens of doubtful composition are valueless. ' 

Curing Specimens. — All cement and mortar specimens will be left in the mold s 
in the moist closet for 24 hours. The laboratory assistant will then remove from 
molds and place the specimens in the proper rack in a bath of running water. 
vSpecimens will remain in the water bath until tested. 

Concrete specimens will remain in the molds for two days; they will then be 
sprinkled twice a day until two weeks old. 

Testing Specimens. — Before testing any specimen the student should read 
carefully Methods jor Testing Cement, page 48-49. No attempt should be made to 
use a briquette testing machine until instruction in the method of operation has 
been obtained. In general, such instruction will be. given at the beginning of the 
exercise at which tests on the first batch of specimens are due. 

In testing cubes, on account of the non-parallelism of the faces of the molds* 
it will be necessary to apply pressure to the tops and bottoms of the specimens . 
If the top and bottom surfaces of compression specimens are uneven they can 
be made plane by the use of a coarse rasp. Bed all compression specimens on two 
thicknesses of blotting paper at top and bottom. Use a centering template and 
spherical bearing block, and be sure that the axis of the block coincides with that 
of the testing machine. 

Reports. — Follow the standard outline in writing reports. The description 
of each experiment should be complete in itself, and should contain a brief resume 
of the method, the data, curves, and computations as required. Copying the 
standard specifications or portions of these notes is unnecessary; simply refer 
to the page giving the description wanted. 

Test C 1. Tensile and Compressive Tests of Mortars Differing in Richness 
of Mixture. 

Materials. — A bank sand from Janesville, Wis. and Portland cement (ascer- 
tain brand). 

Apparatus.— Regular bench equipment — burette, cup, pail, dust-pan, brush- 
scoop, and a 6-inch pointing trowel; 4 sets of cast iron briquette molds; 8, 2> 
inch cast iron cube molds; clamps, tins, and boards for both kinds of molds. 
Test. — (a) Make 16 briquettes as follows: — 

4, neat, using 22 per cent, of water, by weight 
4, ic:is, " 13 " " " " 
4, ic:3s, " 9 " " " " 
4, 1C.5S, o 

The percentages of water are based upon the total weight of sand and cement. 
In computing the quantities of materials required to make four briquettes the 

following table giving weights in grams will be found useful: 

Material ic:is ic:3S ie:5s 

Cement 300 150 [00 

Sand 300 450 500 

Break all briquettes when 28 days old. 

(1)) Make 8, 2-inch cubes as follows: — 

4, neat, using 22 per cent, of water, l>v weight 
4, ic:3s " 13 " ' " " 



29 Laboratory Notes 

Report. — Draw a sketch of a Riehle automatic shot briquette testing machine 
and briefly describe the method of operating it. 

(a) Plot a curve with the breaking strengths of briquettes as ordinates and the 
proportions of sand to cement as abscissas; use for scales i in.=ioo lb. per sq. 
1 n. and I in.= i part sand to I part cement. 

(b) Plot points on the curve sheet with ages as abscissas and unit breaking 
strengths of the cubes as ordinates, and connect the points for the same mix 
with straight lines. Suggested scales are i in. = 5 days and 1 in. = 1000 lb. 
per sq. in. Find the ratio of the unit compressive to unit tensile strength at 
28 days for each mix. 

References :-Johnson — Par. 406, 407, 409; Taylor and Thompson — Page 
132-147. 



Test C 2. The Standard Commercial Test of Portland Cement. 

Materials. — Standard Ottawa sand and a given brand of Portland cement. 

Apparatus. — Regular bench equipment and the following apparatus for the 
respective tests: — (a) Vicat needle apparatus, glass plate and ring; (b) glass 
plates, boiler for accelerated test; (c) 4, 4-gang briquette molds, clamps, etc.; 
(d) No. 100 and 200 sieves, scales sensitive to 0.01 gram, weights, sheets of smooth 
paper; (e) specific gravity flask, kerosene, scales used in (d). 

Test. — (a) Normal Consistency and Time of Set. Before beginning the test 
the instructor will illustrate the method of determining the normal consistency 
and time of set and will show how pats for the soundness test should be made- 

*Using the Vicat needle apparatus, first determine the normal consistency 
for your cement. Refer to page 43 if in doubt concerning the method. After 
determing the normal consistency, smooth off top of specimen and set the glass 
and specimen in the moist closet. Test the specimen for initial set at 15 min- 
intervals. Record the time of initial set. The time of final set may be gotten 
from the instructor. 

(b) Soundness. — From the remainder of the paste used in (a) make, as quickly 
as possible, 3 pats. Place the pats in the moist closet immediately after making 
The pats will be tested in accordance' with the standard method on page 49. 
Note the time at which they should be examined. 

At the proper time examine the pats and ascertain if they have cracked, warped, 
left the glass, broken the glass, of if they have become discolored. In case the 
pats have cracked or warped, make a sketch showing the same. Consult W. P. 
Taylor's Practical Cement Testing or R. K. Meade's Portland Cement and 
ascertain the significance of your results. 

(c) Tensile Strength. — Mold 8 briquettes of neat cement and 8 briquettes of 
one part cement to three parts standard Ottawa sand. Follow carefully the 
directions given on page 45. Obtain the percentage of water required for the 
mortar briquettes from the table on page 44. Break 4 neat briquettes at 7 



*Another convenient way for determining the normal consistency, called the 
ball method, has been adopted by the United States Government. The testis 
made as follows : — Employing the same method of mixing and molding as above, 
quickly form a 2-in. ball of neat cement paste. Drop the ball from a height of 
2 ft. upon the table top. Normal consistency obtains when the ball does not 
crack and does not flatten more than one-half its original diameter. 



on the Strength of Materials 30 

days; test the remainder at 28 days. At the time the briquettes are broken note 
the position and inclination of the line of fracture. If there are large differences 
f in the breaking strengths of the briquettes from the same mix, determine the 
dimensions of the minimum cross-section and ascertain the approximate posi- 
tion and size of any large air holes present in the fracture. Satisfy yourself 
concerning the effect of any flaws upon the strength of the briquettes. 

With careful manipulation in making, curing, and testing the briquettes should 
be 1 x 1 in. at the minimum cross-section, free from large air holes, and the strength 
of any individual briquette should not vary more than 10 per cent, from the aver- 
age for the set. 

(d) Fineness Test. — Be sure that the scales are leveled and placed where 
they will not be subjected to currents of air. The sieves should be carefully 
examined to ascertain if they are in perfect condition before the test is begun • 
In making the test, follow the method specified on page 42 ; take particular pains 
to shake the sieve as directed throughout the test. The final weighing to de- 
termine the percent, held on a sieve should be done on the residue in the sieve. 
In making trial weights, the cement in the pan may be turned onto a smooth 
piece of paper and emptied into the scale pan. Great care should be taken to 
prevent the loss of cement during sifting or weighing. Compute the results to 
the nearest 0.1 per cent. 

(e) Specific Gravity Test. — On account of the small importance of this 
test, it will ordinarily be omitted. If it is made, the method outlined on page 
40 should be employed. If accurate results are to be gotten, it is of great im- 
portance that the temperature of apparatus, liquid, and cement be the same 
throughout the test. Consequently the test should be conducted in a room of 
constant temperature, and both materials and apparatus should be placea in 
the room several hours previous to the test. 

Report. — Fill out the standard blank provided for this test. Compute the 
ratio of the average unit strength of the 1 :3 standard sand mortar briquettes to 
the 1 :3 bank sand mortar briquettes test of Ci. Explain the result. * Should 
your cement be accepted or rejected? Why? 



*The Interpretation of Results of Commercial Tests on Portland Cement 

The student should always bear in mind that the tests are only of qualitative value for the pur- 
pose of comparing the sample with a standard, adopted after long experience, or to compare it 
with previous samples of the same brand of cement. Therefore, before accepting or rejecting a 
cement, he should carefully consider the relative value of the results of each test and the conditions 
under which the cement is to be used. Furthermore, one should not condemn a sample unless 
certain that the conditions surrounding each test were standard. Any uncertainty in regard to 
a result should be removed by performing a second test under standard conditions. Below will 
be found a brief discussion of the criteria determining the acceptability of Portland cement 
arranged in order of the importance of the various tests. 

Soundness. — Reject the cement if the air pat or the water par shows signs of disintegration at 
28 days. If the sample fails to pass the accelerated test but does pass the normal tests, make a 
second accelerated test at 28 days. Failure of the second steam pat test, coupled with any retro- 
gression in neat tensile strength, is sufficient cause for rejection. (Some large firms will not accept 
cement which does not pass the accelerated test although tin- other results are satisfactory. Re- 
cently the Delaware, Lackawanna & Western R. R, has demanded cement which will p iss a still 
more Btringenl an derated test. Sec Engineering News, June 13, 1912, page [in.) 

Tensile Strength. — Reject the cemenl if the strengths at 28 days are less than required by the 

specifications. If the strength of the mortar briquettes it .'8 days is less than at 7 days, reject. 
If the strengths Of mat ami mortar briquettes are a tritle below tin- Standard at 7 days but nv 
above at *>K days, accept the cement. 



31 Laboratory Notes 

References:- Johnson — Par. 313, 314, 323-325; Taylor and Thompson — Ch- 
VII; Taylor— Ch. IV, Page 46-50, 55-62, 63-70, 75-79, Ch. VIII, Ch. IX 
Ch. X; Meade— Page 166-170, Ch. XII, Ch. XVI. 

Test C 3. Compressive Strengths of Concrete Cylinders of Different Propor- 
tions. 

Materials. — Crushed stone or gravel, sand, and Portland cement. Ascertain 
the kind of stone, sand, and cement and the location of the stone and sand de- 
posits. 

Apparatus. — Voidmeter half full of water; weight per cubic foot apparatus; 
12, 6x 18-in. cylinder molds; 4 square-pointed shovels; 1 scoop shovel for filling 
molds; 2 platform scales sensitive to yi lb.; 6, 14-quart galvanized iron pails; 
a couple of steel rods 3 ft. long; a mason's trowel. 

Test. — Before performing this experiment the class will find the weight per 
cubic foot of the sand, of the stone, and of a 1 .2 mixture of sand and stone. The 
class should also determine the per cent, of voids in this mixture. 

Weight Per Cubic Foot. — To find the weight per cubic foot fill the hopper of the 
weight per cubic foot apparatus with material, open the gate in the bottom and 
allow the material to flow into the standard measure at a rate of one cu. ft 
per min. After the measure is full strike off with a straight edge and weigh, 
deducting weight of measure. 

Percentage of Voids. — Find the per cent, of voids by slowly pouring ]4 cu. ft, 
of the 1 :2 mixture of sand and stone into the voidmeter which has been partly- 
filled with water. Pvead the scale before and after placing the material in the 
in the apparatus. 

Calculation of Quantities. — Compute the weight per cu. ft. of each materia 
and determine the per cent, of voids in the aggregate (the sand and stone). 

The class will now be divided into four groups. Each group will make one of 
the following sets of cylinders: — 

3 cylinders of 1 part cement, 1 T /i parts sand, 3 parts stone 

a it 11 <( a " A " " 

(( a it .< n u g a it 

a tt - it it tt «( q " << 

The above proportions are based upon the volumes of dry materials. In 



If judgment must be passed upon a sample at the end of 7 days, reject on a decidedly low mortar 
test. Hold for 28 days if the neat strength is very high or if either the mortar or the neat strength 
is slightly below the standard. 

Time of Set. — -If the cement does not pass the specifications in the laboratory test, determine 
its behavior under conditions in which it will be used before condemning it. Slow final 
set many times accompanies coarseness, which will also affect the tensile strength of the mortar 
briquettes. 

Fineness.— Inasmuch as no sieves made at the present time are sufficiently fine to determine 
the percentage of flour, the important cementing element, this test has only corrobora- 
tive value. Generally, a coarse cement will exhibit a low mortar strength and will oftentimes 
fail in the soundness test. Cements failing in the fineness test should not be accepted before the 
28 day tests are made. , 

Specific Gravity.— Like the fineness test, the specific gravity is oftentimes of corroborative value. 
Its chief value is to detect adulteration when the average specific gravity is known. Such 
adulteration may affect the mortar tensile strength and cause unsoundness. The import- 
ance of this test is small. 

For further information on interpretation of results of cement tests, consult W. P. Taylor ' 
Practical Cement Testing or R. K. Meade's Portland Cement. 



on the Strength of Materials 32 

figuring the amounts of materials necessary use this rule (allowing in labo- 
ratory experiments 15 percent, for waste): — 

* r>_ 1-55 



-s+g 



P = the part of a cubic foot of cement necessary to make a cubic foot of con- 
crete. 

c = number of parts of cement. 

s = number of parts of sand. 

g = number of parts of stone or gravel. 

The amount of stone required = P x g (cubic feet). 

The amount of sand required = P x s (cubic feet) . 
Or, for small quantities of concrete, compute the volume of the stone equal to the 
volume of molds and the amount of sand and gravel based upon it. This gives, 
where there is little waste, a volume of concrete slightly larger than required. 
Compute the weights of the volumes needed and show to the instructor before 
weighing the quantities. 

Mixing and Molding. — Weigh the required amounts of materials in the pails 
provided for the purpose. Select a clean portion of the cement floor near the 
molds, spread the sand upon it, and cover the sand with a layer of cement. In 
accordance with the directions of the instructor, turn the material 3 times. Spread 
the stone, which has been previously wetted, upon the mixture and turn 
twice. Form a crater in the pile and add sufficient water to make a wet mix — 
about 9 or 10 per cent, of the total weight of the dry materials. Place the concrete 
in the molds and puddle with a rod to prevent pocketing of materials and to bring 
the mortar to the surface. This not only adds greatly to the appearance of the 
cylinder but makes it more dense. Leave the top of the concrete slightly lower 
than mold. This will be capped with a 1 :i mortar, on the day after the experi- 
ment is completed, to obtain a smooth, even bearing surface. 

Breaking. — Break all cylinders at 28 days, using one of the large machines. 
Place two sheets of blotting paper upon each of the compressed surfaces of the 
specimens and use spherical tools. Be sure that the axis of the machine, spherical 
block and specimen are collinear. 

Report. — Tabulate in your report the unit breaking strength of each cylinder 
and the average of each set of three. Compute the ratio of the volume of cement 
to the volume of voids in the aggregate for each set of cylinders. Plot a curve 
with unit breaking stresses as ordinates and the ratio of the volume of cement 
to the volume of voids in the aggregate as abscissae. For scales use 1 in. =400 
lb. per sq. in. and 1 in. =0.2. 

References:- Johnson — Par. 4i8-425a; Taylor and Thompson — Page 354-398, 
183-193, 210-215. 

Test C 4. Cross Bending Test of a Reinforced Concrete Beam.t 

Materials. — Broken stone or gravel, sand, Portland cement, and steel rod s 
8 ft. 11 in. long for reinforcing the beam. Determine the kind, location o\ de- 
posit, and size of stone; do likewise for the sand; also find out the weight per cu. 
ft. of the stone and of the sand, and obtain the percent, of voids in each. Ascer- 



* A modification of Puller's rule, 
t Class experiment. 



33 Laboratory Notes 

tain the brand and results of tests on the cement. The physical properties of 
the reinforcement should also be gotten. 

Apparatus. — For making the beam, there will be used a batch mixer of 6 cu. 
ft. capacity (equipped with hopper cart, scales, and water- weighing-device), 
a channel-iron beam mold, two 6 x i8-in. cylinder molds, trowels and rods for 
puddling the concrete, and wheel-barrows for conveying the concrete. 

In testing the beam, the ioo,ooo-lb. Olsen transverse testing machine will 
be used together with a wire-mirror-scale deflect ometer; in some cases, deforme- 
ters for measuring the deformations in the upper and lower fibers of the beam 
will also be employed. 

Test. — .Making. By the formula given in test C3, calculate the quantities of 
material required for a volume of 1 :2 4 concrete 10 per cent, in excess of the volume 
of cylinder and beam molds. Weigh out all materials in the car placed on the 
charging scales, start the motor, discharge the contents of the car into the mixer 
and mix the dry materials for oie minute. Turn on the water, weighing out 
by means of the graduated scale a sufficient quantity to make a wet concrete 
(9 or 10 percent, of total weight of sand, cement, and stone). Discharge the con- 
tents of the mixer into the wheelbarrows when the total time of mixing is 3 min- 
utes. 

Cover the bottom of the mold with concrete to a depth of 4^ in. and place the 
rods in position as directed, jostle the concrete about them with a trowel and 
fill the mold. Run a trowel around the sides of mold to form a smooth surface and 
level off the top. Also make two cylinders from the same batch of concrete. 

Breaking. Unless otherwise specified, break the specimens at 28 days. Make 
a sketch of the beam showing dimensions, size and location of reinforcement, the 
kind of reinforcement, the method of loading, and the position of the apparatus 
for measuring deflections and deformations. 

Apply loads in predetermined increments and take readings of deflections and 
deformations as directed. Be sure to note the load at the first visible crack and 
at the ultimate. Determine the load-deformation curve of one concrete cylinder 
in compression and note the breaking strength of each. 

Report. — Compute the modulus of elasticity of the concrete cylinder at a 
stress of 500 lb. per sq. in. from a crave drawn with unit stresses and deformations 
as ordinates and abscissae, respectively. Employ as scales 1 in. =200 lb. per sq. 
in. and 1 in. =.0002 in. per in. 

Find the unit stress in the beam on the extreme fibre of concrete in compression 
and on the steel at the load at which the first crack appeared. Use the "Straight 
Line Formula" (see page 52), for this computation; for the modulus of elasticity 
of steel use 30,000,000 lb. per sq. in. Take the modulus of elasticity of concrete 
from the cylinder test. [If deformeters were used, compute the unit stress in the 
steel from the elongation at the first crack, and compare with the result obtained 
from the formula.] 

Compute the factors of safety in tension and in compression, basing your 
calculation upon the ultimate strength of the concrete and the elastic limit of 
the steel. Also compute by the "Parabolic Formula" (see page 54) the unit 
stresses in the concrete and steel at the ultimate load. If the beam failed by 
compression, compare the computed unit stress in the concrete with the average 
ultimate strength of the cylinders; if a tension failure obtained, compare the com- 
puted unit stress in the steel with the elastic limit of the steel. [If deformeters 
were employed, compare the unit stress in the steel derived from ultimate defor- 
mations with that computed from the formula.] 



on the Strength of Materials 34 

References :-Page 50 to 54; Taylor and Thompson — Page 477-483. 

Test C 5. Tests for Determining the Quality of Different Sands. 

Materials. — Four kinds of sand numbered 1 to 4 and Portland cement. Find 
out the locality from which each sand was obtained and use the same brand of 
cement as in test C 2. 

Apparatus. — Regular bench equipment and the following for the respective 
tests: — (a) 4, 4-gang briquette molds; (b) 12, 2-in. cube molds; (c) large as- 
pirator bottle, 1 2-in. percolator, rubber tubing, one or more clean 10-gallon cans, 
evaporating pan, Bunsen burner, scales sensitive to 0.0 1 gram; (d) sieves No. 
4, 6, 10, 20, 30, 50 and 100, mechanical shaker; (e) small yield test cylinder and 
tamper, scales sensitive to 0.0 1 lb. 

Test. — The class may well be divided into groups of 3 for this experiment. 
Each group should perform the strength tests on all of the sands and the other 
tests on at least one of the sands. 

(a) Tensile Test. — Make 4, 1:3 mortar briquettes of each sand and break at 
28 days. Determine the normal consistency for each mortar by comparing con- 
sistency of a trial mix with the normal consistency of a standard sand mix. 

(b) Compressive Test. — Make 3, 2-in. cubes of 1 13 mortar of each sand. Use 
the same consistency as in (a) and break at the same age. 

(c) The impalpable dust which may be separated from an aggregate by elutria- 
tion (washing) is called silt. Inasmuch as a large portion of the impurities which 
are harmful to the aggregate is generally found in the silt, it is important to know 
the percent, of silt; and, if the percentage is large, its chemical composition is 
often valuable. The per cent, of silt may be determined as follows: 

Arrange the aspirator bottlcon a shelf so that its spigot will be 3 ft. above the 
lateral outlet on the percolator. The latter should be supported in a ring stand. 
Connect the spigot on the aspirator bottle with the bottom of the percolator and 
cover the orifice in the percolator with a double thickness of No. ioo wire cloth 
to prevent the fine material from entering the tube. Select a representative 
200-gram sample of the material passing through a >4-in. mesh and place it in the 
bottom of the percolator. Fill the aspirator bottle with distilled water, allow the 
water to enter percolator, and catch the overflow in a 10-gallon can. With a 
glass rod stir the material vigorously for 10 sec. at 1 min. intervals. Stop the 
flow when the water above the material ceases to hold any fine particles in suspen- 
sion immediately after stirring. 

Dry the material in granite-iron pans provided for the purpose. After all 
water has been evaporated, scrape the entire residue from pan and weigh. 

(d) Mechanical Analysis Test. — Place the sieves in the mechanical shaker in 
the following order, bottom to top, — 100, 50, 30, 20, 10 and 6. Next pour a 
representative 2000-gram sample of dry sand onto the No. 6 sieve, fasten down 
the cover securely, and start, the motor. At the e id of 10 min. stop the shaker; 
weigh and record the total amount held on each sieve, also secure tne diameter of 
opening for each sieve. 

(e) Yield Test. — From the yield test the weight per cu. ft. of the mortar, the 
ratio of the volume of mortar to the volume of aggregate, and, with the specific 
gravities of the cement and sand known, the density of the mortar may be gotten. 
The procedure in testing follows. 

Weigh on scales, sensitive to 0.01 lb., 0.75 ll>. of c. -incut and 2.25 He o\ sand. 

Then place the sand in t he yield tct cylinder in layers about 1 ! fin. deep, compact" 



35 Laboratory Notes 

ing each layer with the cast iron tamper. When all the sand is in the cylinder mea - 
sure its volume by means of the plunger and tripod. Mix the dry materials 
thoroughly until a uniform color obtains throughout the mass. Next make a 
mortar of standard consistency and place in the cylinder as before. Record the 
weights and volumes on the blanks furnished for the purpose. 

Report. — Tabulate the results of all tests, the per cent, of voids and the specific 
gravity for each sand. The per cent, of voids and specific gravity values will be 
given by the instructor. From the yield test compute the density of each mix 
(the ratio of the mass of the sand plus cement to the volume of the wet mortar) 
from its weight and specific gravity. Tabulate these values. 

Draw curves showing the relation between unit crushing strength and density 
ana between unit tensile strength and density. 

Plot a curve with unit compressive strengths as ordinates and the ratio of the 
volume of cement to the volume of voids in the sand as abscissae. 

Compute the weight per cu. ft. and the yield for each mortar. 

If cement costs $1.50 per bbl. and any of the sands $1.25 per cu. yd. which is 
the most economical sand, assuming a 1 :3 mix is to be used. 

From the mechanical analyses tests plot curves with the per cent, less than a 
given diameter of mesh, as ordinates, and diameter of mesh in inches, as abscissae. 
The scales suggested are 1 in. = 20 per cent, and 1 in.= 0.05 in, Place all curves 
on the same sheet. Note the difference in the position and shape of the curves 
for the various sands. 

References :-Taylor and Thompson — Ch. IX, Page 168-182; U. S. G. S. 
Bulletin No. 331; Proceedings of the A. S. T. M. 1910 — Page 341, 191 1 — 
Page 515; 



Engineering News Vol. 67 — Page 1022. 
Test C 6. The Effect of the Fineness of Cement Upon the Tensile Strength of 
Mortar. 

Materials. — Use Janesville bank sand passing a K'-in. mesh and provide a 
sufficient quantity of a standard Portland cement to make 8, 1 :3 mortar briquettes 
Weight out enough cement to make 16, 1:3 briquettes and sift it on a No. 200 
sieve until half of the cement has passed through. 

Apparatus. — Six, 4-gang briquette molds and auxiliary equipment, No. 200 
sieve and mechanical cement shaker. 

Test. — Following the standard method of mixing and molding, make 8 bri- 
quettes using the cement as received, 8 briquettes using the cement held on the 
No. 200 sieve, and 8 briquettes using the cement passing the No. 200 sieve. Ten 
per cent, of water may be employed in mixing all mortars. 

Break half of each batch of briquettes at 7 days and the remainder at 28 days. 

Report. — Tabulate and explain your results. At which age is the strength 
of 1 13 mortar briquettes most affected by the fineness of the cement? 

References :- Johnson — Par. 310; Taylor and Thompson — Page 82-85; Taylor- 
Page 105-106. 



Test C 7. The Effect of Grading the Size of Sand Grains Upon the Tensile 
Strength of Mortar. 

Materials. — Portland cement passing the standard specifications and Janes- 
ville bank sand screened and classified as follows: 



on the Strength of Materials 36 

Large grains, G, passing a No. 6 and retained on a No. 16 mesh; 
Medium grains, M, " " " 16 " " " " " 40 " ; 

Fine grains, F, " " " 40 sieve. 

Apparatus. — Five, 4-gang brass briquette molds and auxiliar}^ equipment. 

Test. — In this test it is advisable to divide the class into groups of three. Each 
group should perform the program given below. 

Use 10 per cent, of water; mix and mold in accordance with the standard method 

4, 1:3 briquettes of sand G; 

4, 1 :3 briquettes of sand M ; 

4, 1 :3 briquettes of sand F; 

4, 1:3 briquettes, using sand consisting of 1 part F, 1 part M and 1 part G; 

4, 1 :3 briquettes, using sand consisting of 1 part F, 1 part M and 3 parts G. 

Be sure that the proportions of sand and cement are correctly weighed. When 
the briquettes are taken from the moist closet the average weight of each set 
ofU should be determined. 

The tests should be made at 28 days. 

Report. — Tabulate your results and plot a curve with breaking strengths as 
ordinates and average weights of briquettes as abscissa?. What conclusions may 
be drawn from this test: 

References:- Johnson — Par. 410-413; Taylor and Thompson — Page 147-154, 
Ch. X. 

Test C 8. The Standard Commercial Test of Natural Cement. 

Perform a regular commercial test on natural cement. Follow the method 
outlined in C 2 but do not make an accelerated soundness test. Also read care- 
fully the specifications on page 37. 

Fill out a standard blank for this test. 

Should the cement be accepted or rejected? State the reason for your answer. 

References :-Taylor — Page 252-263. 



VI. STANDARD SPECIFICATIONS FOR CEMENT. 

ADOPTED BY THE AMERICAN SOCIETY FOR TESTING MATERIALS, 

AUGUST 16, 1909. 

GENERAL observations. 

1. These remarks have been prepared with a view of pointing but the per- 
tinent features of the various requirements and the precautions to be observed 
in the interpretation of the results of the tests. 

2. The Committee would suggest that the acceptance or rejection under thes 
specifications be based on tests made by an experienced person having the prope 
means for making the tests. 

SPECIFIC GRAVITY. 

3. Specific gravity is useful in detecting adulteration. The results of tests 
of specific gravity are not necessarily conclusive as an indication of the quality 

of a cement, bul when in combination with the results cf other tests may afford 

valual lie indications. 

FINENESS, 

4. The sieves should be kept thoroughly dry. 



r 



1a~ ::- -_t: :-:: V :rzs 



z .::ei: tare sh:ali Ir e~erm ; 
tmiitims as c-t-s-smle. A saiie: 
::■::". a: ~la;h the tests am mar 
irregularities vitally affect the rat 

CC> St. 

6. The tests far constancy of 

armaai rhe set-mi aateleratei. 
r::aam t -: r t : m v, =,— ^ arr maallm 

5'; n:ir^:tTiii :: :: ~~~~ :r sa: 



SETTING. 

aamtam :: 



me imaiei in": e~: : lasses, the am: 
mter shaali he mrariei as = are tan- 
ma r •" ~ -' enter mt: ""- "--. -: — : g 
isei ~th r::::~t tare, 
are shaali he tIt:::^. :: am:i :mtiai 
irymt-mm iamag the firs: : — earn-:: a: 



_ at failm- 



sa ::ea: :aas< 



:aase ::r re;e:ta:m 
saii mat rath :laila 

rmslirrei emirelv 



.meats :: the ateelerarei tes:s aeei am :e 
e~e-: mav m — men be heli :':: :~ent/- 
r eni ::' ~*m.~ :r~:: mar a ae — =i~:^ 
this time shaali be ::mmem-i ; - : — — _~- 

: resent state ::' :ur kn:— ieme it ;aaa :: be 



SPECIFICATIONS. 



:— : 



r ;: 



r — 



.A" :eraem shah be haste: aei. 

iemea: am :e msaemer earner at :if:^;t :t ~- a m 
m mier :: all : — amtie rime ::r msaerrma _i: rest: 

aei in t ;.:tt: ~ ear :t:-::j:;.: b.mimr having The 
sen mem the m: mi. 

The erm: shall be sttrei in sa:h a manner as a: 
r msaeraim aa i iienriaaatita ::' eath shmmenr. 

amery ratmhy s~a" be ammie: by :he I mrratttr aa i a aermi :t at iea=: 
e lays ah:~ei fm the mstemara ani ae:essary :es:s 

rentent shall be ieliverei in saitable aaiaates -mm the braai mil name 
nmattmer alaialy aaar'aei thereon. 

A bag ::' temea: shah rmraia :_ t: anas :: zemen: ae: Zm . t-arrei :: 
tni temen: shth tmtain ± mts mi eath tarrei :: narnaal iTtiea - shall 



rmmaime: :n "nit: ma 
eers tres-entei : : the c 
ani January 15, 1908,1 



::. _ae a:: 

11. Denniti 

resul:mt "" ~ 

rntitient : : :m 



a:s 



— - =-- = " ~r 



a: a te: 



on the Strength of Materials 38 

fineness. 

12. It shall leave by weight a residue of not more than 10 per cent, on the 
No. 100, and 30 per cent, on the No 200 sieve. 

TIME OF SETTING. 

13. It shall not develop initial set in less than ten minutes; and shall not de- 
velop hard set in less than thirty minutes, or in more thai three hours. 

TENSILE STRENGTH. 

14. The minimum requirements for tensile strength for briquettes one square 
inch in cross-section shall be as follows, and the cement shall show no retrogression 
in strength within the periods specified: 

Age Neat Cement Strength. 
24 hours in moist air 75 lbs. 

7 days (1 day in moist air, 6 days in water) 150 " 

28 days (1 " " " 27 " " ) 250 " 

One Part Cement Three Parts Standard Ottawa Sand 

7 days (1 day in moist air, 6 days in water) 50 lbs. 

28 days (1 " " " 27 " " ) 125 " 

CONSTANCY OF VOLT ME. 

15. Pats of neat cement about three inches in diameter, one-half inch thick 
at center, tapering to a thin edge, shall be kept in moist air for a period of twenty- 
four hours. 

(a) A pat is then kept in air at normal temperature. 

(b) Another is kept in water maintained as near 70° F. as practicable. 

16. These pats are observed at intervals for at least 28 days, and, to satis- 
factorily pass the tests, shall remain firm and hard and show no signs of distortion, 
checking, cracking, or disintegrating. 

PORTLAND CEMENT. 

17. Definition. This term is applied to the finely pulverized product result- 
ing from the calcination to incipient fusion of an intimate mixture of properly 
proportioned argillaceous and calcareous materials, and to which no addition 
greater than 3 per cent, has been made subsequent to calcination. 

SPECIFIC GRAVITY. 

18. The specific gravity of cement shall not be less than 3.10. Should the 
test of cement as received fall below this requirement, a second test may be made 
upon a sample ignited at a low red heat. The loss in weight of the ignited cement 
shall not exceed 4 per cent. 

FINENESS. 

19. It shall leave by weight a residue of not more than 8 percent, on the No. 
100, and not more than 25 per cent, on the No. 200 sieve. 

TIME OF SETTING. 

20. It shall not develop initial set in less than thirty minutes; and must de- 
velop hard set in not less than one hour, nor more than ten hours. 

TENSILE STRENGTH. 

21. The minimum requirements for tensile strength for briquettes one square- 
inch in cross-section shall be as follows, and the cement shall show no retrogres- 
sion in strength within the periods specified: 



39 Laboratory Notes 

Age Neat Cement Strength 
24 hours in moist air 175 lbs. 

7 days (1 day in moist air, 6 days in water) 500 " 

28 days (1 " " " 27 " " ) .600 " 

One Part Cement, Three Parts Ottawa Sand. 

7 days (1 day in moist air, 6 days in water) 200 lbs. 

28 days (1 " " " 27 " " ■ ) 275 " 

CONSTANCY OF VOLUME. 

22. Pats of neat cement about three inches in diameter, one-half inch thick 
at the center, and tapering to a thin edge, shall be kept in moist air for a period 
of twenty-four hours. 

(a) A pat is then kept in air at normal temperature and observed at intervals 
for at least 28 days. 

(b) Another pat is kept in water maintained as near 70 F. as practicable 
and observed at intervals for at least 28 days, 

(c) A third pat is exposed in any convenient way in an atmosphere of steam, 
above boiling water, in a loosely closed vessel for five hours. 

23. These pats, to satisfactorily pass the requirements, shall remain firm and 
hard, and show no signs of distortion, checking, cracking, or disintegrating. 

SULPHURIC ACID AND MAGNESIA. 

24. The cement shall not contain more than 1.75 per cent, of anhydrous 
sulphuric acid (S0 3 ), nor more than 4 per cent, of magnesia (MgO). 



VII. ADDENDUM. 

METHODS FOR TESTING CEMENT.* 

Recommended by the Special Comittee on Uniform Tests of Cement of 
the American Society of Civil Engineers. 

Sampling. 

1. — Selection of Sample. — The selection of samples for testing should be left 
to the engineer. The number of packages sampled and the quantity taken from 
each package will depend on the importance of the work and the facilities for 
making the tests. 

2. — The samples should fairly represent the material. When the amount to 
be tested is small it is recommended that one barrel in ten be sampled ; when the 
amount is large it may be impracticable to take samples from more than one barrel 
in thirty or fifty. When the samples are taken from bins at the mill one for each 
fifty to two hundred barrels will suffice. 

3. — Samples should be passed through a sieve having twenty meshes per linear 
inch, in order to break up lumps and remove foreign material; the use of this 
sieve is also effective to obtain a thorough mixing of the samples when this is 
desired. To determine the acceptance or rejection of cement it is preferable 
when time permits, to test the samples separately. Tests to determine the gen- 
eral characteristics of a cement, extending over a long period, may be made with 
mixed samples. 



Tinal report — see Proc. A. S. C. E. Feb. 19 12, page 103. 



on the Strength of Materials 40 

4. — Method of Sampling. — Cement in barrels should be sampled through a 
hole made in the head, or in one of the staves midway between the heads, by 
means of an auger or a sampling iron similar to that used by sugar inspectors; 
if in bags, the sample should be taken from surface to center; cement in bins should 
be sampled in such a manner as to represent fairly the contents of the bin. Samp- 
ling from bins is not recommended if the method of manufacture is such that in- 
gredients of any kind are added to the cement subsequently. 

Chemical Analysis. 

5. — Significance .—Chemical analysis may serve to detect adulteration of cement 
with inert material, such as slag or ground limestone, if in considerable amount. 
It is useful in determining whether certain constituents, such as magnesia and 
sulphuric anhydride, are present in inadmissible proportions. 

6. — The determination of the principal constituents of cement, silica, alumina, 
iron oxide, and lime, is not conclusive as an indication of quality. Faulty cement 
results more frequently from imperfect preparation of the raw material or defective 
burning than from incorrect proportions. Cement made from material ground 
very finely and thoroughly burned may contain much more lime than the amount 
usually present, and still be perfectly sound. On the other hand, cements low 
in lime may, on account of careless preparation of the raw material, be of danger- 
ous character. Furthermore, the composition of the product may be so greatly 
modified by the ash of the fuel used in burning as to affect in a great degree the 
significances of the results of analysis. 

7. — Methods. — The methods to be followed, except for determining the loss 
on ignition, should be those proposed by the Committee on Uniformity in the 
Analysis of Materials for thePortland Cement Industry, reported in the Journal 
of the Society for Chemical Industry Vol. 21, page 12, 1902; and published in 
Engineering News Vol. 50, p. 60, 1903; and in Engineering Record, Vol. 48, p. 
49. l 9°2» an d in addition thereto, the following: 

(a) — The insoluble residue may be determined as follows: To a 1 -gramme 
sample of the cement are added 30 cu. cm. of water and 10 cu. cm. of concentrated 
hydrochloric acid, and then warmed until effervescence ceases, and digested on a 
steam bath until dissolved. The residue is filtered, washed with hot water, and 
the filter paper and contents digested on the steam bath in a 5 per cent, solution 
of sodium carbonate. This residue is filtered, washed with hot water, then with 
hot hydrocholric acid, and finally with hot water, and then ignited at a red heat, 
and weighed. The quantity so obtained is the insoluble residue. 

(b) — The loss on ignition shall be determined in the following manner: % 
gramme of cement is heated in a weighed platinum crucible, with cox-cm-, for 5 
minutes with a Bunsen burner (starting with a low flame and gradually increasing 
to its full height) and then heated for 15 minutes with a blast lamp; the difference 
between the weight after cooling and the original weight is the loss on ignition. 
The temperature should not exceed 900 cent., or a low red heat; the ignition 
should preferably be made in a muffle. 

Specific Gravity. 
N. — Significance. — The specific gravity of cement is lowered by adulteration 

and hydration, hut, the adulteration must he Considerable to he detected by tests 
of specific gravity. 

9. — Inasmuch as the differences in specific gravity arc usually very small 
greal care must he exercised in making the determination. 



41 



„AZ ' ?vAT :ry X:iZ5 



10. — Appar::?. — The i-Tem:ir_a: :::; :: spe :ih: grs-viry ~h . maie :. 

a -eandardized Le Chatelier apparatus. This consists ©f a flasfr (D) t Fig. 3 
of about 120 cu. cm. capactiy, the neck, of which is about 20 cm. long; in the 
middle of this neck is a bulb (O, above and below which are two marks (IT) and 
(E) ; the volume between these two marks is 20 cu. cm. The neck has a diameter 
of about 9 mm., and is graduated into tenths of cubic centimeters above the mark 




FIG. 1. LE 



XEFIC GRAVITY APPARATUS. 



ns/rhrha :r kerzsene free :r:m ~a.rer sheuli 



. 



II. — Benzine r2 iegree; 3es.-.i: 
're ust! in nir.ki-g the iererrnina: 

12.— Method.— The nask i; n_e 
E anf. :_ rcrarrmzes ::' :errenr. :::leir: :ke temperature :■: the z.:.::i. is ;l:~ly 
introduced through the funnel (B), (the stem of which should be long enough to 
extend into the flask to the top of the bulb (C), taking care that the cement 
does not adhere to the sides of the flask, and that the funnel does not touch the 
liquid. After all the cement is introduced, the level of the liquid will rise to some 
division of the graduated neck; this reading, plus 20 cu. cm., is the volume, dis- 
placed by 64 grammes of the cement. 



on the Strength of Materials 



42 



13. — The specific gravity is then obtained from the formula 

Specific gravity = _Weight of cement, in grammes, 



Displaced volume, in cubic centimeters. 

14. — The flask, during the operation, is kept immersed in water in a jar (A), 
in order to avoid variations in the temperature of the liquid in the flask, which 
should not exceed 1° cent. The results of repeated tests should agree within 
0.01. The determination of specific gravity should be made on the cement as 
received; if it should fall below 3.10, a second determination should be made 
after igniting the sample in a covered dish, preferably of platinum, at a low red 
heat not exceeding 900 cent. The sample should bs hsatsd for 5 minutes with a 
Bunsen burner (starting with a low flame and gradually increasing to its full 
height) and then heated for 15 minutes with a blast lamp; the ignition should pre- 
ferably be made in a muffls. 

15. — The apparatus may be cleaned in the following manner: The flask is 
inverted and shaken vertically until the liquid flows freely, and then held in a 
vertical position until empty; any traces of cement remaining cai be removed 
by pouring into the flask a small quantity of clean liquid bsnzine or ksrossns and 
repeating the operation. 

Fineness. 

16. — Significance. — It is generally accepted that the coarser particles in cement 
are practically inert, and it is only the extremely fine powder that possesses 
cementing qualities. The more finely cement is pulverized, other co iditions bsing 
the same, the more sand it will carry and produce a mortar of a given strength. 

17. Apparatus. The fineness of a sample of cement is determined by weigh- 
ing the residue retained on certain sieves. Those known as No. 100 and No. 200, 
having approximately 100 and 200 wires per linear inch, respectively, should 
be used. They should be 8 in. in diameter. The frame should be of brass, 8 in. 
in diameter, and the sieve of brass wire cloth conforming to the following require- 
ments. 

The meshes in any smaller space, down to 0.25 in., should be proportional in 
number. 



No. of sieve. 


Diameter of wire. 


Meshes per Linear Inch. 




Warp 


Wcof. 


100 
200 


0.0042 to 0.0048 in. 
0.0021 to 0.0023 " 


95 to 101 
192 to 203 


93 to 103 
190 to 205 



18. Method. The test should be made with 50 grammes of cement, dried 
at a temperature of ioo° cent. (212 Fahr.). 

19. — The cement is placed on the No. 200 sieve, which, with pan and cover 
attached, is held in one hand in a slightly inclined position, and moved forward 
and backward about 200 times per minute, at the same time striking the side 
gently, on the Up stroke, against the palm of the other hand. The operation is 
continued until not more than 0.03 gramme will pass through in one minute 
The residue is weighed, then placed on the \'«>. 100 sieve, and the operation re- 
peated. The work may he expedited by placing in the sieve a. tew Large steel 
shot, which should he removed before the final one minute of sieving. The sieves 
should he thoroughly dry and clean. 



43 



Laboratory Notes 



Normal Consistency. 

20. — Significance. — The use of a proper percentage of water in making pastes* 
and mortars for the various tests is exceedingly important and affects vitally 
the results obtained. 

21. — The amount of water, expressed in percentage by weight of the dry 
cement, required to produce a paste of plasticity* desired, termed "normal con- 
sistency," should be determined with the Vicat apparatus in the following man- 
ner: 

22. — Apparatus. — This consists of a frame (A), Fig. 4, bearing a movable 
rod (B), weighing 300 grammes, one end (C) being 1 cm. in diameter for a distance 
of 6 cm., the other having a removable needle (D), 1 mm. in diameter, 6 cm. long. 
The rod is reversible, and can be held in any desired position by a screw (E), and 
has midway between the ends a mark (F) which moves under a scale (graduated 
to millim eters) attached to the frame (A). The paste is held in a conical, hard- 
rubber ring (G), 7 cm. in diameter at the base, 4 cm. high, resting on a glass plate 
(U) about 10 cm. square. 




9 s 

F 



%E 



PH 



FIG. 4. VICAT APPARATUS 

23. — Method. — In making the determination, the same quanticy of cement 
as will be used subsequently for each batch in making the test pieces, but not less 
than 500 grammes, with a measured quantity of water, is kneaded into a paste, 
as described in Paragraph 45, and quickly formed into a ball with the hands, 
completing the operation bv tossing it six times from one hand to the other, main- 
tained about 6 in. apart; the ball resting in the palm of one hand is pressed into 



*The term ' ' paste ' ' is used in this report to designate a mixture of cement 
and water, and the word "mortar" to designate a mixture of cement sand and 
water. 



on the Strength of Materials 



44 



the larger end of the rubber ring held in the other hand, completely filling the ring 
with paste; the excess at the larger end is then removed by a single movement 

of the palm of the hand ; the ring is then placed on its larger end on a glass plate 

and the excess paste at the smaller end is sliced off at the top of the ring by a 

single oblique stroke of a trowel held at a slight angle with the top of the ring. 

During these operations care must be taken not to compress the paste. The 

paste confined in the ring, resting on the plate, is placed under the rod, the larger 

end of which is brought in contact with the surface of the paste; the scale is then 

read, and the rod quickly released. 

24. — The paste is of normal consistency when the cylinder settles to a point 
10 mm. below the original surface in one-half minute after being released. The 
apparatus must be free from all vibrations during the test. 

25. — Trial pastes are made with varying percent" s of water until the norma 
consistency is obtained. 

26. — Having determined the percentage o± water required to produce a paste 
of normal consistency, the percentage required for a mortar containing, by 
weight, one part of cement to three parts of standard Ottawa sand, is obtained 
from the following table, the amount being a percentage of the combined weight 
of the cement and sand. 

Percentage of Water for Standard Mortars. 





One cement. 




One cement, 




One cement, 


Neat. 


three standard 


Neat. 


three standard 


Neat. 


three standard 




Ottawa sand. 




Ottawa sand. 




Ottawa sand. 


15 


8.0 


23 


9.3 


31 


10.7 


16 


8.2 


24 


9.5 


32 


10.8 


17 


8.3 


25 


9.7 


33 


11.0 


18 


8.5 


26 


9.8 


34 


11.2 


19 


8.7 


27 


10.0 


35 


11.3 


20 


8.8 


28 


10.2 


36 


11.5 


21 


9.0 


29 


10.3 


37 


11.7 


22 


9.2 


30 


10.5 


38 


11.8 



Time of Setting. 

27. — Significance. — The object of this test is to determine the time which 
elapses from the moment water is added until the paste ceases to be plastic 
(called the "initial set"), and also the time until it acquires a certain degree of 
hardness (called the "final set" or "hard set"). The former is the more impor- 
tant, since, with the commencement of setting, the process of crystallization be- 
gins. As a disturbance of this process may produce a loss of strength, it is desir- 
able to complete the operation of mixing or moulding or incorporating the mortar 
into the work before the cement begins to set. 

28. — Apparatus — The initial and final set should be determined with the Yicat 
apparatus described in Paragraph 22. 

2C). — Method. — A paste of normal consistency is moulded in the hard-rubber 
ring, as described in Paragraph 23, and placed under the rod (/?), the smaller 
end of which is then carefully brought in contact with the surface oi the paste 
and the rod quickly released. 

30. The initial set is said to have occurre I when the needle ceases to pass a 

point 5 mm. above the glass plate; and the dual set, when the needle ilors nut 
sink visibly into the paste. 



45 



Laboratory Notes 



31. — The test pieces should be kept in moist air during the test; this may be 
accomplished byplacing them on a rack "over water contained in a pan and covered 
by a damp cloth; the cloth to be kept from contact with them by means of a 
wire screen ; or they may be stored in a moist box or closet. 

32. — Care should be taken to keep the needle clean, as the collection of cement 
on the sides of the needle retards the penetration, while cement on the point may 
increase the penetration. 

33. — The time of setting is affected not only by the percentage and tempemture 
of the water used and the amount of kneading the paste receives, but by the tem- 
perature and humidity of the air, and its determination is, therefore, only approxi- 
mate. 

Standard Sand. 
34. — The sand to be used should be natural sand from Ottawa, 111., screened 
to pass a Xo. 20 sieve, and retained on a Xo. 30 sieve. The sieves should be at 
least 8 in. in diameter; the wire cloth should be of brass wire and should con- 
form to the following requirements: 



No. of sieve. 


Diameter of wire. 


Meshes per Linear Inch. 




Warp. 


Woof. 


20 
30 


0.016 to 0.017 in. 
0.011 to 0.012 " 


19.5 to 20.5 
29.5 to 30.5 


19 to 21 
28.5 to 31.5 



Sand which has passed the No. 20 sieve is standard when not more than 5 
grammes passes the Xo. 30 sieve in one minute of continuous sifting of a 500- 
gramme sample.* 

Form of Test Pieces. 

35. — -For tensile tests the form of test piece shown in Fig. 5 should be used. 

36. — For compressive tests, 2-in. cubes should be used. 

Moulds. 

37. — The moulds should be of brass, bronze, or other non-corrodible material, 
and should have sufficient metal in the sides to prevent spreading during moulding. 

38. — Moulds may be either single or gang moulds. The latter are preferred 
by many. If used, the types shown in Figs. 6 and 7 are recommended. 

39. — The moulds should be wiped with an oily cloth before using. 

Mixing. 

40. — The proportions of sand and cement should be stated by weight; the quan- 
tity of water should be stated as a percentage by weight of the dry material. 

41. — The metric system is recommended because of the convenient relation of 
the gramme and the cubic centimeter. 

42. — The temperature of the room and of the mixing water should be main- 
tained as nearly as practicable at 21 cent. (70 Fahr.). 

43. — The quantity of material to be mixed at one time depends en the number 
of test pieces to be made; 1,000 grammes is a convenient quantity to mix by hand 
methods. 



*This sand may now (19 12) be obtained from the Ottawa Silica Co., at a 
cost of two cents per pound, f. o. b. cars, Ottawa, 111. 



on the Strength of Materials 



46 







1.5" _._ 


1 










1.3" 








1 1 

1 1 
1 1 

1 
1 1 






\ 

■ \ 
1 \ 
















<■ ' ^^ .' \ 


1 " ^ 

1 ' !^ 

1 if ! 

! / < 
1 ■ 

I f ' 

I I < 

if ' 
if 1 

f 1 






1 \ 
1 \ 


\ 
\ 

\ 

\ 

\ 
\ 

V 

\ 
\ 
\ 
\ 
\ / 


\ / \l 1 

\ / V 1 

\ / A \ 
* * 


Vgf 






"Vh! 


/%) 


x / 


1 ■* — '1 








/,_\, 


\ / 


\ j Bad- 








/V 


\ f 
\ f 


Up—; 

11 ^^ 


1 

« 

• 

1 
1 
« 


^^^^ 


/ 

/ 


/4? 

/ 

/ 


s I 
\ f 

\ / 

\ #1 


^.„ 










^ ^^ \ / 


1 

<- 






__ja — 




^ 








— I — 












"r*\ 












V 







FIG. 5. — DETAILS FOR BRIQUETTI 




CXXXXXXX)- 



/ 



55 



h'HJ.6. — DETAILS FOR (JANG MOl'LDS. 




PIG. 7. —MOULD FOR COMPRESSION TEST PIECES. 



47 Laboratory Notes 

44. — The Committee has investigated the various mechanical mixing machines 
thus far devised, but cannot recommend any of them, for the folio woing reasons : 
(1) the tendency of most cement is to "ball up" in the machine, thereby prevent- 
ing working it into a homogeneous paste; (2) there are no means of ascertaining 
when the mixing is complete without stopping the machine; and (3) it is difficult 
to keep the machine clean. 

45. — Method. — The material is weighed, placed on a non-absorbent surface 
(preferably plate glass), thoroughly mixed dry if sand be used, and a crater formed 
in the center, into which the proper percentage of clean water is poured ; the ma- 
terial on the outer edge is turned into the center by the aid of a trowel. 
As soon as the water has been absorbed, which should not require more than 
one minute, the operation is completed by vigorously kneading with the hands 
for one minute. During the operation the hands should, be protected by rubber 
gloves. 

Moulding. 

46. — The Committee has not been able to secure satisfactory results with exist- 
ing moulding machines; the operation of machine moulding is very slow; and is 
not practicable with pastes or mortars containing as large percentages of water 
as herein recommended. 

47. — Method. — Immediately after mixing, the paste or mortar is placed in the 
moulds with the hands, pressed in firmly with the fingers, and smoothed off with 
a trowel without ramming. The material should be heaped above the mould, 
and, in smoothing off. the trowel should be drawn over the mould in such a man- 
ner as to exert a moderate pressure on the material. The mould should then be 
turned over and the operation of heaping and smoothing off repeated. 

48. — A check on the uniformity of mixing and moulding may be afforded by 
weighing the test pieces on removal from the moist closet; test pieces from any 
sample which vary in weight more than 3 percent, from the average should not 
be considered. 

Storage of the Test Pieces. 

49. — During the first 24 hours after moulding, the test pieces should be kep 
in moist air to prevent drying. 

50. — Two methods are in common use to prevent drying: (1) covering the 
test pieces with a damp cloth, and (2) placing them in a moist closet. The use 
of the damp cloth, as usually carried out, is object ionable, because the cloth may 
dry out unequally and in consequence the test pieces will not all be subjected 
to the same degree of moisture. This defect may be remedied to some extent 
by immersing the edges of the cloth in water; contact between the cloth and the 
test pieces should be prevented by means of a wire screen, or some similar arrange- 
ment. A moist closet is so much more effective in securing uniformly moist 
air, and is so easily devised and so inexpensive, that the use of the damp cloth 
should be abandoned. 

51. — A moist closet consists of a soapstone or slate box, or a wooden box lined 
with metal, the interior surface being covered with felt or broad wicking kept 
wet, the bottom of the box being kept covered with water. The interior of the 
box is provided with glass shelves on which to place the test pieces, the shelves 
being so arranged that they may be withdrawn readily. 

52. — After 24 hours in moist air, the pieces to be tested after longer periods 
should be immersed in water in storage tanks or pans made of non-corrodible 
material. 



on the Strength of Materials 



48 



53. — The air and water in the moist closet and the water in the storage tanks 
should be maintained as nearly as practicable at 21 cent. (70 Fahr.) 




SECTION A B 

I>olier turned andaccuratelj 

bored to easy turning fit 



FIG. 8. FORM OF CLIP. 



Tensile Strength. 

54. — The tests may be made with any standard machine. 

55. — The clip is shown in Fig. 8. It must be made accurately, the pins and 
rollers turned, and the rollers bored slightly larger than the pins so as to turn 
easily. There should be a slight clearance at each end of the roller, and the pins 
should be kept properly lubricated and free from grit. The clips should be used 
without cushioning at the points of contact. 

56. — Test pieces should be broken as soon as they arc removed from the water. 
Care should be observed in centering the test pieces in the testing machine, as 
cross strains, produced by imperfect < entering, tend to lower the breaking strength. 
The load should not be applied too suddenly, as it may produce vibration, the 
shock from which often causes the test piece to break before the ultimate strength 
is reached. The bearing surfaces of the clips and test pieces must be kepi free 
from grains of sand or dirt, which would prevent a good bearing. The load should 
be applied at the rate of 000 lb. per min. The average of the results o\ the test 

pieces from each sample should be taken as the test of die sample Test pieces 



49 



Laboratory Notes 



which do not break within T 4 in. of the center, or are otherwise manifestly faulty, 
should be excluded in determining average results. 

Compressive Strength. 

57. — The tests may be made with any machine provided with means for so 
applying the load that the line of pressure is along the axis of the test piece. 
A ball-bearing block for this purpose is shown in Fig. 9. Some appliance should 
be provided to facilitate placing the axis of the test piece exactly in line with the 
center of the ball-bearing. 

58. — The test piece should be placed in the testing machine, with a piece of 
heavy blotting paper on each of the crushing faces, which should be those that 
were in contact with the mould. 




Head of Testing Machine 



FIG. 9. — -BALL-BEARING BLOCK FOR TESTING MACHINE. 



Constancy of Volume. 

59. — Significance. — The object is to detect those qualities which tend to des- 
troy the strength and durability of a cement. Under normal conditions these 
defects will in some cases develop quickly, and in other cases may not develop 
for a considerable time. Since the detection of these destructive qualities before 
using the cement in construction is essential, tests are made not only under normal 
conditions but under artificial conditions created to hasten the development 
of these defects. Tests may, therefore, be divided into two classes: (1) Normal 
tests, made in either air or water maintained, as nearly as practicable, at 21° 



on the Strength of Materials 50 

cent. (70 Fahr.); and (2) Accelerated tests, made in air, steam or water, at tem- 
perature of 45 cent. (113° Fahr.) and upward. The Committee recommends 
that these tests be made in the following manner: 

60. — Methods.— Pats, about 3 in. in diameter, ]/ 2 in. thick at the center, and 
tapering to a thin edge, should be made on clean glass plates (about 4 in. square) 
from cement paste of normal consistency, and stored in a moist closet for 
24 hours. 

61. — Normal Tests. — After 24 hours in the moist closet, a pat is immersed in 
water for 28 days and observed at intervals. A similar pat, after 24 hours in the 
moist closet, is exposed to the air for 28 days or more and observed at intervals. 

62. — Accelerated Tests. — After 24 hours in the moist closet, a pat is placed 
in an atmosphere of steam, upon a wire screen 1 in. above boiling water, for 5 
hours. The apparatus should be so constructed that the steam will escape freely 
and atmospheric pressure be maintained. Since the type of apparatus used has 
a great influence on the results, the arrangement]shown in Fig. 10 is recommended. 

63. — Pats whch remain firm and hard and show no signs of cracking, distor- 
tion, or disintegration are said to be "of constant volume" or "sound." 

64. — Should the pat leave the plate, distortion may be detected best with a 
straight-edge applied to the surface which was in contact with the plate. 

65. — In the present state of our knowledge it cannot be said that a cement 
which fails to pass the accelerated test will prove defective in the work; nor can 
a cement be considered entirely safe simply because it has passed these tests. 

VIII. FLEXURE FORMULAS 

FOR 

REINFORCED CONCRETE BEAMS. 

The following discussion has been taken from Turneaure and Maurer's Prin- 
ciples of Reinforced Concrete Construction, Ch. III. 

"Notation. — Fuller explanations of some of these symbols are given in sub- 
sequent articles where the formulas are derived; see also Fig. n. 

/ s denotes unit fibre stress in steel; . 

/c " " concrete at its compressive face; 

en " elongation of the steel due to f s ; 

g ( . " shortening of the concrete due to f e ; 

£« " modulus of elasticity of the steel; 

E c " " the concrete in compression; 

n ratio E a / Ee\ 

T total tension in steel at a section of the beam; 

C total compression in concrete at section of the beam; 

Ms " resisting moment as determined by steel; 

M v " resisting moment as determined by concrete; 

M bending moment or resisting moment in general; 

h " breadth of a rectangular beam; 

d " distance from the compressive face to the plane ^\ the steel; 

k " ratio of the depth of the neutral axis of a section below the top to </.' 

j " ratio of the arm of the resisting couple to d; 

A " area of cross-section of steel; 

p " steel ratio, .1 bd." 



5i 



Laboratory Notes 



-n- 



A\ 



y- 



« © 

•3.- 



\ 



• 5/ U- 



— a e! 



/r 



M J 



-XS-*l 



/r 



^? 



rt 



-?i- 



k-S- 
1 // 

^9— 



B 



TTT 



^ 



-SI- 



\ 



2 o 
< 

CO 















j " ~? 




















































-, 












-- 














. 




















































" 











3g 



_ i 



B< s 



-si 



Z 

S O 

<r 

u. 




._* 



~tP 






* o 



'*•- 




eqm jaqqtu aiqixau * ( 



JIDOQ ipnk£ 



on the Strength of Materials 



52 



"Flexure Formulas for Working Loads Based on Linear Variation 
of the Compression and Neglecting Tension in the Concrete. — The 
loads being working loads, the unit stress in the steel is within the elastic limit, 
and the unit stresses in the concrete vary as the ordinates to the compressive 
stress-strain curve for concrete up to working stresses. This curve is nearly- 
straight; it will be assumed straight to simplify the formulas. " (The resulting 
errors are small, as is explained in Art. 70. Turneaure & Maurer's Principles 
of Reinforced Concrete Construction). 

''Neutral Axis and Arm of Resisting Couple.— It follows from the assump- 
tion of plane sections that the unit deformations of the fibers vary as 
„ , their distances from the neu- 

~^ — * "*— tral axis; hence, 

e s / ec = (d — kd) / kd, see Fig. 1 1 . 
Also e s = f / E s and e c =/ c / £c ; 
hence, introducing the abbre- 
viation n, 




/s __d — kd 
nfc kd 



[a] 



When the loads and reactions 
are vertical — beam horizontal 
— the total tension and compres- 
FIG j j sion on the section are equal, i-e. 

f s A=lf c bkd [b] 

Eliminating / s // c between equations (a) and (b) and introducing the abbrevia- 
tion p gives 2 pn (1 — k) =k 2 ; this if solved for k gives 

k = \/2pn -j- (pn) 2 — pn . . . . [1] 

This formula shows that the neutral axes of all beams of a given concrete and of 
a given percentage of reinforcement are at the same proportionate depth, k, for 
all working loads." 

"The distance of the centroid of the compressive stress from the compressive 
face of the beam is \kd\ therefore the arm of the resisting couple, TC, is given by 

jd = d — ^kd or j=l — \k .... [2] 

As k increases, j decreases, but not in the same ratio." 

"Resisting Moment for Given Working Stresses f and f c . — If the beam is 
under-reinforced, its resisting moment depends on the steel and its value then is 

M s =T-fd=f s A-jd = f s pjbd 2 . . . . [3] 
If over-reinforced, the resisting moment depends on the concrete and its value 
then is 

Mr = Cjd=} 2 fcbkd-jd=lfrkjbd- . . . f 4 ] 

To find the resisting moment in a given case, these values of M must be compared • 
and the lesser one taken; but it may be noticed that a comparison of the quan- 
tities f%p and J^/.k is sufficient to determine which of the values is the lesser. 
* For approximate computations one may use the average values /=| ami 
lc = \ ; then formulas [3] and [4] become respectively 

M*-M'ld t fo'l 

A/ H = /,■>>/'-' | 4 i| 

"Unit Fibre Stresses for a Given Bending Moment.-— Formulas for these may 



* Do not use in computations unless so instructed. 



53 



Laboratory Notes 



be obtained from equations [3] and [4] by solving them for f s and f c respectively; 
M= (Ms or M c ) will denote bending moment." 

"Flexure Formulas for Ultimate Loads, Based on Parabolic Varia- 
tion of Compression and Neglecting Tension in Concrete. — It is assumed 
that the amount of reinforcement is sufficient to develop the full compressive 
strength of the concrete without straining the steel beyond its yield point; or 
otherwise expressed, failure occurs by crushing of the concrete, the stress in the 
steel being still within the yield point. Then the parabola representing the varia- 
tion of compression is a full parabola, the upper end (see Fig. 12) being trie vertex." 



f\ fc 




FIG. 12. 



"If the amount of steel in a beam is such that the ultimate strength of the con- 
crete and the elastic limit of the steel would be reached simultaneously if the 
beam were subjected to a gradually increasing load, then this will be called the 
ideal amount — no better term seems available — but this amount may not be the 
best in a given case." 

"In the present connection, the two following properties of a parabola like 
that of Fig. 12 are useful: [1] The average abscissa of the parabolic arc equals 
two-thirds the greatest f c ; [2] the distance from the centroid of the parabolic 
area to its top equals three-eights the total height, kd." 

''Neutral Axis and Arm of Resisting Couple. — The 'initial modulus of 
elasticity' of the concrete is denoted by E c in the present article. It is repre- 
sented by the tangent of the angle between the vertical through N and the tangent 
to the stress strain curve at N. And since NA represents e c , it follows from 
a well-known property of the parabola that fe = /4E K ec. Also fs = E s e s , and from 
the assumption of plane sections it follows that e s / e c — (d — kd) / kd. Eliminating 
e s / e c from the above equations, and introducing the abbreviation, n gives 

f s - I ~ k [a] 



-the total tension 



2nf c k 

When the loads and reactions are vertical — beam horizontal- 
and the total compression on the section are equal, i. e., 

f s A=ifobkd (b) 

Eliminating / s If between equations [a] and [b] and introducing the abbrevia- 
tion p, gives 3pn = k 2 / (1 — k); this if solved for k gives 

k = i/ 3pn + (ipny~—%vn .... [5] 
This formula shows that the neutral axes of all beams of a given concrete and of 



on the Strength of Materials 54 

a given ' percentage of reinforcement are at the same proportionate depth, k, 
for their respective ultimate loads." 

"The distance of the centroid of the compressive stress from the compressive 
face of the beam is |kd; therefore the arm of the resisting couple TC, is given by 

jd=d—%kd, orj = i— |k . [6] 

Plainly, as k increases./ decreases, but not at the same rate." 

"Ultimate Resisting Moment for a Given Ultimate Strength f c . — Remember- 
ing the assumption made at the outset in regard to the amount of steel, it will be 
understood that the ultimate resisting moment always depends on the concrete; 
the value is . 

M< = C.jd=l^bkdjd = ?jkf c bd 2 . . [7] 

It should be remembered that this equation gives the ultimate resisting moment 
only if when the unit stress in the concrete is at the ultimate that in the steel is 
not beyond the elastic limit." 

"If the beam has the 'ideal amount' of reinforcement before referred to, then 
the ultimate resisting moment can be computed from the steel by means of 

M 5 =T.jd=f s A.jd=f s pjbd* .... [8] 

in which f s denotes elastic limit of steel." 

* u For approximate computations one may use the average values j= 0.8 and 
£ = 0.52; with these, formulas (7) and (8) become respectively 

M c =o.278f c bd* . . . [?'] 

M s = To.8d = o.8f s pbd 2 . . . [8'] 

Unit Fibre Stresses For Ultimate Resisting Moment. — Formulas for these 
stresses may be obtained from equations (7) and (8) by solving them for f c and 
fs respectively; M ( = M S or M c ) will denote bending moment. 



IX. THE MANUFACTURE OF PIG AND CAST IRON 

The Ores of Iron. — Neither pure iron nor the commercial products, such as 
cast iron, wrought iron, or steel occur free in nature. It is, therefore, necessary 
to reduce the ores of iron in order to obtain the ferrous metals. In order of their 
commercial importance in the United States the chief ores of iron are; red hem- 
atite (Fe 2 :! ), brown hematite or limonite (2 Fe 2 : ,, 3KLO), magnetite (Fe ; ,0 4 ) 
and spathic ore or ferrous carbonate (FeCO s ). 

Red hematite contains, theoretically, 70 per cent, of iron. However, owing 
to various impurities and the presence of water of crystallization the best ores 
of this oxide contain only 50 to 60 per cent, of iron. In the United States red 
hematite from the Lake Superior region constitutes about four-fifths of the annual 
production of iron ore. Spain, Germany and England also have large deposits 
of this ore. 

Brown hematite in accordance with the chemical formula contains about 60, 
per cent, of iron. On account of reasons similar to those given for red hematites, 
the biown hematites of this country are much leaner than the formula indicates. 
In color the limonites vary from a brownish black to a yellowish brown. These 
ores form the most abundant supply of iron ore in the United States, but they 
are very poor in iron. Alabama, Virginia, Tennessee, and Georiga furnish con- 
siderable quantities of brown hematite. 

Magnetite is the richesl and hardest iron ore containing, in perfect form, 72.4 

*Do not use in computations unless so instructed. 



55 Laboratory Notes 

per cent, of iron. It is a black metallic oxide which is strongly attracted bv the 
magnet. The most important and the purest deposits of this ore are found in 
Sweden. In the United States, Xew York, Pennsylvania, and New Jersey lead 
in the production of magnetite. The chief obstacle to the use of magnetite in 
this country is the impurity of the deposits. Many large sources of supply are 
contaminated by titanium oxide. However, it is believed by leading metallurg- 
ists that the difficulties now encountered in separating this oxide of iron from 
titanium oxide will soon be solved and large deposits of this rich ore, which have 
hitherto been considered worthless, may then be advantageously mined. 

Ferrous carbonate is a gray or brown ore containing 37.9 percent, of iron. In 
an impure state, it forms a considerable part of the ore deposits of England. 
Only a very small amount of this ore is mined in the United States, Ohio being the 
chief source of supply. 

Mining and Transportation — In many ranges where the ore is of a soft earthy 
nature running near the surface, mining is carried on in open cut by means of 
steam shovels. The hard ores and those more deeply imbedded beneath the 
glacial drift are worked by the underground methods of caving and slicing, over 
hand stoping, or by the method of milling, which is a combination of under- 
ground and surface methods. The rich and soft ores require but little preliminary 
treatment before shipment to the blast furnace. The hard ores are crushed by 
means of gyratory or jaw crushers; ores contaminated by clay or sand are fre- 
quently washed; those containing large quantities of volatile matter are roasted. 

In as, much as coke, the fuel commonly used in reducing the ores, depreciates 
considerably in value if subjected to a long railroad journey, ore is generally car- 
ried to the region supplying the coke. In the Lake Superior district ore cars 
are run from the mines to the wharves where they are emptied into large storage 
bins. From these bins the material may be spouted into the holds of ore 
barges. These barges, many of which have capacities of 10,000 tons, carry the 
ore to the southern end of Lake Michigan or to one of the many ore receiving ports 
on Lake Erie. The barges are unloaded with great rapidity by means of 10-ton-grab 
buckets. At some ports these buckets are connected to cabs traveling on a hori- 
zontal crane so arranged that the ore may be carried directly to the stock pile of 
an adjacent blast furnace plant. At other ports the ore is loaded into cars and 
shipped to the blast plant. To secure maximum economy in transportation, 
great speed must be maintained in loading and unloading so that the barge may 
be delayed in port as short a time as possible. Records have been made in which 
large barges were unloaded at the rate of over 2000 tons per hour. 

The Blast Furnace. — The first step in modern practice in the manufacture of 
ferrous metals is the reduction of the ores to pig iron by means of the blast fur- 
nace. A general idea of the shape of a blast furnace may be gotten from Fig. 
13, provided one remembers that the cross-section is circular and that the inside 
of the steel shell is lined with silica fire brick. Although blast furnaces vary 
somewhat in size, modern designers appear to have adopted a height of about 
100 feet and a diameter cf approximately 22 feet at the top of the bosh. Such 
a furnace will discharge 450 to 500 tons of pig iron per 24-hour day. At the right 
of Fig. 13 is shown the storage bins containing fuel, ore, and flux. These materials 
are elevated to the top of the furnace by skips running on the incline shown at 
the right. At the top the charge is automatically dumped into tne double bel] 
and hopper arrangement. The operation of this hopper is such that the material 
can be lowered and spread uniformly over the charge within the furnace without 
creating a direct connection between the interior and the open air. 



on the Strength of Materials 



56 




57 Laboratory Notes 

At the bottom of the furnace, the straight cylindrical portion 7 or 8 ft, high 
carrying the molten metal, is called the crucible or hearth. This is lined with 
refractory brick and is encased in a water cooled jacket as shown in Fig. 14. 
Placed in front and at the extreme bottom of the hearth is the tap hole through 
which the molten metal is drawn off. A similar orifice, called the cinder notch, 
is located on the side of the furnace about midway up the hearth. The cinder 
notch is provided to drain off the slag which, being lighter than the molten metal, 
floats on top of the bath. Both of these holes are plugged by clay balls when 
not in use. Just above the cinder notch and below the top of the hearth, is placed 
a circumferential row of nozzles which extend radially through the furnace wall 
and connect with a large bustle pipe running around the outside of the furnace. 
Through these nozzles or tuyeres a hot blast of air, which supplies oxygen to 
accelerate the combustion of the fuel, is forced into the furnace. The hot waste 
gases pass out at the top of the furnace through a large pipe, called a downcomer. 
This is provided with a trap for catching the dust carried along by the gas. 

The fuel used in the blast furnace must be both strong and porous. It must 
also furnish an intense heat without producing an ash containing large amounts 
of phosphorus or sulphur, elements which are undesirable in either iron or steel- 
Coke, the solid residue produced by distillation of the volatile matter from bitumi- 
nous coal, is the most satisfactory and most widely used fuel. 

The flux must also be comparatively free from phosphorus, sulphur, or other 
injurious elements. It must also be strongly basic in character, since its function 
is to unite with and make fluid the earthy portions of the ore and the ash of the 
fuel, both of which generally give acid reactions. On account of its cheapness 
and wide distribution, limestone is most commonly used as a flux. 

In order to secure a specified grade of pig iron it is necessary that the chemical 
analysis of the ore charged, as well as that of the flux and fuel, be predeter- 
mined. The proper proportioning of the chemical ingredients in the ore is gen- 
erally accomjished by mixing different grades. 

Tne proportions of the charge vary considerably at different plants, depending 
on the grade of ore and its gangue. With the best grades the charge is about 
one-sixth limestone, one-third fuel, and the remainder ore. The pig iron tapped 
from such a charge will amount to about 50 per cent, of the ore. 

Hot Blast Stoves. — In order that the blast furnace might be run most efficiently 
it was found necessary to preheat the blast. At the present time this is accomp- 
lished in hot blast stoves. A hot blast stove consists of a steel shell about 100 
ft. high and 20 ft. in diameter which is lined with fire brick. Fig. 15 shows a 
sectional elevation of a hot blast stove. The interior of the stove is divided into 
a large number of small vertical compartments built of fire brick and one or more 
large vertical combustion chambers. The hot waste gas from the blast furnace and 
a carefully regulated blast of cold air enter at the bottom of the combustion 
chamber. These burn, pass upward to the top of the stove and then downward 
through the small compartments to the chimney flue, heating the walls of the 
stove in passage. After one stove has been sufficiently heated, the hot gas is 
diverted to another and the cold blast from the blowing engine is blown through 
the reheated stove on its way to the blast furnace. The blast is thus heated to a 
temperature of about iooo F. before it enters the furnace. Four stoves are 
commonly used in the operation of one furnace; one heats the blast while the 
others are being heated. 

The Manufacture of Pig Iron. — The blast entering the tuyeres contains 77 
percent, oxygen and 23 per cent, nitrogen. The nitrogen enters into no chemical 



ON THE STRENGTH OF MATERIALS 58 

reaction in the furnace. The oxygen at once combines with the carbDi in th? 
coke and forms CO with an evolution of much heat. Measurements by Le 
Chatelier show a temperature of 3500 F. at the top of the hearth. As this 
gas rises it meets alternately layers of ore and fuel. From the ore it extracts 
oxygen forming C0 3 , and from the fuel it obtains carbon, reducing the CO., to 
CO. In addition to forming chemical reactions the gas also gives up heat to the 




MMUM 



FIG. 14. — SECTIONAL ELEVATION OF BLAST FURNACE SHOWING DE 
TAILS ok HEARTH AND BOSH CONSTRUCTION. 



burden. As a result of these changes, the wastegas passingoff through the down- 
comer has a temperature of perhaps jot. 1 ' P. and eonsists largely of a mixture 
of CO, CO., and N. This waste gas forms one of the important by-products 

ot th- blast furnace process. At some plants pari <>\ the gas is washed and used 



59 



Laboratory Notes 



to run gas engines for blowing the blast or producing power, part is burned under 
boilers, and part is used to reheat the hot blast stoves. 

The blast furnace is continually being charged with fuel, flux, and ore, deposited 
in rotation, and with sufficient speed to keep the level of the burden within seven 
or eight feet of the bell and hopper. As the fresh ore descends it is gradually 
robbed of its oxygen by the ascending CO, until at the middle of the furnace it has 
become a mass of spongy iron which absorbs carbon from the fuel in its downward 




SECTIONAL ELEVATION 



FIG. 15. MCCLURE PATENT HOT BLAST STOVE. 

NOTE:— The Arrows show the passage of the air on its way to the blast furnace. 

passage. By the absorption of carbon the iron is rendered more fusible. Con- 
sequently it soon melts and trickles down through the fuel and slag into the 
hearth, absorbing silicon and some sulphur, and retaining most of the phosphorus 
and manganese found in the ore. Near the middle of the furnace the limestone 



ON THE wSTRENGTH OF MATERIALS 



60 



loses C0 2 . The infusible residue calcium oxide, combines with the alumina and 
silica present in the ore and forms a fusible slag covering the bath in the crucible. 
Lime also unites with sulphur to form calcium sulphide, which is dissolved in the 
slag. Consequently a high sulphur content in an ore may be greatly reduced 
by properly proportioning the flux. 

While the iron is running into the hearth it is frequently necessary to remove 
the slag which floats on top of the bath. This is accomplished by unplugging the 
cinder notch. At some plants the escaping slag is run through a trough to slag 
buggies and carried to the slag dump; at others the slag is granulated by running 
while hot into a large tank or vat of cold water. At the present time granulated 
slag is used as an aggregate for making concrete, as a raw material in the man- 
ufacture of cement and mineral wool, and as an ingredient in making paint. 

As soon as a sufficient amount of iron has collected in the hearth the slag is 
again drawn off through the cinder notch. Then the tap hole at the bottom of 
the furnace is broken open and a hundred or more tons of molten pig iron run off. 
The molten stream is skimmed of any entrained slag and is either cast into pigs 
or conveyed molten to open hearth furnaces or Bessemer converters, in which 
it is made into seel. The older method of casting into pigs consists in running 
the metal into sand molds formed in the floor in front of the blast furnace. In 
many modern plants the molten iron is conveyed to pig casting machines fitted 
with metal molds for the reception of the iron. A common tyre of this machine 
is shown in Fig. 16. 




FIG. !<"). DOUBLE STRAND UEHLING PIG CASTING MACHINE. 
A, LADLE-BUGGY TRACK; B, SHIPPING fRACK. 

The Manufacture of Cast Iron. Although iron from the blast furnace is some- 
times used to make castings, nearly all pig iron is remelted in a cupola or in an 

air furnace before being cast into its final shape. This is necessitated by the 
Variability [n successive blast furnace charges and by the fact that pig nun from 



6i 



Laboratory Notes 



a given furnace must of ten be mixed with that obtained from a distance in order 
to secure the proper grade or metal in castings. The cupola is a sort of small 
blast furnace. It consists of a vertical cylindrical steel shell of nearly uniform 
diameter lined with fire brick. Fig. 17 shows an elevation of a common type 




I TAPPING HOLE 



FIG. 17. — CUPOLA. 



of cupola. At the bottom is located the hearth or crucible extending upward, 
a short distance to the level of the tuyeres. The cupola is provided with a hole 
for tapping the slag and a tap hole is placed at the bottom of the crucible to drain 
off the metal. For charging, a door is placed somewhat above the middle of the 
furnace. The charge, consisting of alternate layers of coke and graded pig iron, 
and in some foundries a very little limestone flux, is piled in the cupola to the level 
of the charging door. If the cupola is being started, wood is first placed on the 
hearth to kindle the lowest layer of coke. After the wood has burned and the 
coke has caught fire an air blast of about one pound per sq. in. is admitted through 
the tuyeres. This produces rapid combustion of the coke and an intense heat 
which rapidly melts the pig iron. The ascending gases pass up through the cupola 



on the Strength of Materials 62 

and heat the charge above. It will be readily appreciated that the intensity 0} 
the blast pressure and the thickness of the layers of coke and iron must be care- 
fully regulated if the cupola is to be efficiently run. The appearance of the 
flame issuing from the stack and the rapidity with which iron begins to flow from 
the tap hole after admission of the blast furnish valuable indications of the action 
of the cupola. In melting, iron and silicon are lost by oxidation and more or 
less sulphur is absorbed from the coke. 

The air furnace which is often used to make malleable iron castings or to pro- 
duce castings running very closely to a given analysis is a reverberating furnace 
similar to that employed in puddling wrought iron, shown in Fig. 19. Soft coal 
is burnt on the hearth and a fores draft is employed to acclerats combustion 
In the air furnace process more fuel is required than in the cupola process, but 
the amount of sulphur taken up from the hot gases, used to heat the metal, is much 
less than that absorbed from coke in the cupola. Furthermore, the silicon and 
carbon content are under much better control in the air furnace than in the cupola 

One of the most recent developments in the metallurgy of cast iron is the appli- 
cation of the regenerative open hearth furnace to the production of high grade 
castings. This process, however, is long and quite expensive and has not yet 
come into general use. 

X. THE MANUFACTURE OF WROUGHT IRON AND 

STEEL. 

Production Statistics. — In consideration of the great value of the ores of iron and 
the products manufactured from them, a brief summary of the more important 
statistics relating to the iron industry follows. 

Approximately one-fourth of the pig iron made in the United States is remelted 
and molded into cast iron; the remainder is purified and made into steel or wrought 
iron. In order that a conception of the United States' output of the different 
ferrous metals may be gotten, Fig. 18 has been prepared. It will be ob- 
served that the output of cast iron and steel is greater than the total pig iron 
tonnage. This is due to the use of scrap in the foundry and in the open hearth 
processes. It is also of interest to note that the United States produced about 
43 percent, of the world's supply in 1910. The value of the enormous product 
of this country was $425,115,235. 

1. METHODS OF MANUFACTURE OF WROUGHT IRON. 

Direct Method of Extraction from Ores. — The reduction of either ores or pig 
iron to the ferrous metals is an oxidizing process. Both wrought iron and steel 
may be made directly from iron ore or indirectly by the conversion of pig iron, 
the product of the blast furnace. Owing to the waste of heat, the care required 
in preparing the ores for the furnace, and the loss of iron in the direct process of 
extraction, this method is much more costly than the indirect process. In the 
latter process the ores are reduced to pig iron by the blast furnace before the con- 
version into steel. Although the ancient direct process of extraction has now 
become obsolete, yet on account of historical interest a brief description of this 
process as carried out in the Catalan forge follows. 

The Catalan forge consists of a rectangular sandstone hearth lineal with char- 
coal and provided with side walls of iron. Through one of the side walls a copper 
tuyere having a downward inclination of about 30 degrees serves to admit the 
blast. Small lumps of ore and charcoal are charged into the furnace, the tire 
started, and the blast gradually turned on. The blast of air from the tuyere 



6.; 



Laboratory Xotes 



produces a rapid combustion of the charcoal with a formation of carbon dioxide, 

CO £ . As this carbon dioxide rises it absorbs more car::r_ :r:rz the charcoal 
anz ftrrr.s : :::r. minixize. C '. The lar'tcn m:n:xize vdthdra~s ::■: .gentrcm 
the ore fo rming CO* and metallic iron. After a couple of hours the fluid slag — 
which consists of ferrous oxide, silica, lime, magnesia, manganese oxide and 
phosphorus — is tapped off through a hole in the side of the forge. Soon the 
metalin the ore is completely reduced to spongy masses of iron which the work- 
man collects into balls and passes through a squeezer to remove the entrained 
slag and t: szliiiiy the iron, After the squeezing zr::ess the ir:n is reheated, in 
a sirrulzr tcrge and — irkei unlet a uamnter int: the desired shape. 

5; far as tan :e learned :r:m hist:ri:ai reezrds the direzt :r: :ess ~zs the :rdy 



• Malleable Iron 
/ OOO,0OO* 




^Wrought Iron 

1,740,156 

l.t. 



z - ' --.---:. 




*Aad OH Sreel 

/, 212, 180 

lr. 



FIG. I 5. — PRODUCTION STATISTICS OF THE FERROUS METALS FOR THE 

UNITED STATES. 



on the Strength of Materials 



64 



method of making wrought iron which was known between the years 4000 B. C. 
and 1500 A. D. 

The Puddling Process. — Wrought iron is nearly pure iron containing 
a very small percentage of slag which cannot be entirely eliminated in the process 
of manufacture. This slag, so intimately mixed with the iron during the squeezing 
and rolling process, gives the distinctly fibrous texture commonly observed in the 
fracture of a wrought iron bar. Nearly all of the wrought iron manufacture 
at the present time is made by the puddling process which was patented by Henry 
Cort of England in 1784. 

In Pig. 19 are shown a sectional elevations of a puddling furnace — often called a 
reverberatory furnace. This furnace consists of a grate at one end, a hearth 
with sloping roof occupying the central portion, and a stack, or flue leading to 
the stack, at the end opposite the grate. The outside of the furnace consists 
of cast iron plates tied together by long bolts running on the outside across the 
top of the furnace; the inside of the plates composing the hearth are lined with 
fettling, a material rich in iron oxide. 



miiiiiiiiiiiiiiiiiiiiiiiiiiiiiiir/^ 

SLAG HOLE —WORKING OOOR 



— -- fire-— mm «■ 

i BRIDGE ■«• ^WfffifBiffiWBBi ■■» 



CAST IRON PLATE 




AIR CHAMBER 

< 
SECTION ON C-D 



7 



tjf*}*: 




SECTION ON A-B 



FIG. 19. — SECTIONAL ELEVATION OF TYPICAL DOUBLE PUDDLING FURNACE. 



In operating the furnace a large amount of hammer slag, red oxide of iron, or 
similar material is first uniformly compacted upon the hearth, and then about 
400 or 500 pounds of grey forge iron is added. The fire is now vigorously started 
and the heat produced in the ignition of bituminous coal or gas is deflected by the 
sloping roof upon the charge in the furnace. In about one-half hour the metal 
has all been melted down. During this melting down stage practically all of the 
silicon and manganese, considerable phosphorus, and some sulphur are oxidized. 
To prevent the phosphorus and sulphur from returning to the iron, more mill 
scale or iron oxide is now stirred into the charge. This produces a highly basic 
slag which will further oxidize these elements and hold them in solution. 

In order that proper conditions may obtain for the above reactions, the tem- 
perature of the furnace is reduced by closing the damper in the flue and. if neces- 
sary, by throwing water upon the charge. Finally the iron oxide in the slag 
unites with the carbon in the pig iron, producing carbonic oxide and the mm. 
The latter combines with the iron already in tin- bath, but the former rises and 
causes the bath to swell up like a boiling syrup. As this gas bursts through the 
surface of the charge it burns in little jets of pale blur flame. During the "boil" 
the charge becomes so inflated wit h carbonic oxide that it rises six inches or more 
in the hearth and the larger portion of the sla^ actually Hows over the door sill. 



65 Laboratory Notes 

The overflow is caught and removed by a slag buggy placed to receive it. Since 
the melting temperature of the iron rises as the impurities decrease, the tempera- 
ture of the furnace is gradually raised until, at the end of the boil, the highest 
temperature attainable in a puddling furnace does not suffice to maintain the 
iron in a molten state. The puddler now "rabbles'.' the charge continually with 
a long iron hoe to prevent oxidation of the exposed metal, to prevent it from 
settling on the bottom of the hearth, and to secure as uniform a product as pos- 
sible. Finally all of the iron "comes to nature " and forms a spongy cake of metal 
resting on a bed of slag. The temperature of the furnace is now reduced, and the 
metal cake is broken into five or six pieces by the puddler and his assistant. 
These pieces are worked into balls and removed from the furnace which is now 
prepared for another heat. About five or six heats can be run in a twelve hour 
day. 

To free the iron balls from entrained slag, they are carried from the furnace 
to a squeezer which presses out most of the slag and gives the iron a more uniform 
composition. After removal from the squeezer the balls are rolled into "muck" 
bars. These bars are cut and piled in cross wise layers, reheated and rolled again 
into smaller "merchant" bars — the trade name for wrought iron rounds and 
flats — or into other desired shapes. 

The finished shape then contains not over 0.2 percent, carbon with possibly 
0.3 per cent, of other impurities, slag, phosphorus, sulphur and silicon, as previously 
mentioned. The slag fibres give to the wrought iron the peculiar fracture com- 
monly observed in a tension test. Owing to the fact that much so-called wrought 
iron is now made by reheating a considerable proportion of steel scrap with 
"mu ck" bars, it is quite common to find material which is sold for wrought iron 
exhibiting many of the properties of soft steel. 

2. METHODS OF MAKING STEEL. 

The Cementation Process. — The great affinity which red-hot wrought iron 
possesses for carbon is the basis of the cementation process of converting it into 
steel. In this process the cementing furnace is provided with large converting 
pots made of fire brick which are externally heated from the hearth. Alternate 
layers of charcoal and wrought iron bars are packed in these pots in such a way 
that every bar is surrounded by charcoal. The furnace temperature is very 
slowly raised until it reaches 1200 or 1300 F. at the end of three or four days. 
After this temperature has been maintained for a week or more, depending 
upon the amount of carbon desired in the steel, the fire is drawn and the 
furnace is very slowly cooled. The product is called "blister" steel on account 
of the blisters appearing on the surface of the bars. These bars are sometimes 
piled and worked under the hammer one or more times thus furnishing what is 
known as ' ' shear ' ' steel. On account of the length of time required and the high 
cost of this process it has not been used to any extent in America. In England, 
however, "blister" steel has been considerably employed in the manufacture 
of cutlery and tools. The cementation process for making steel was the only 
one known until 1500 A. D. 

The Crucible Process. — In 1740 Daniel Huntsman of Sheffield, England, made 
an important advance in the manufacture of steel by inventing the crucible 
process. This process consists in the melting wrought iron together with char- 
coal and a little manganese in a small barrel shaped vessel called a crucible. 
Sometimes steel scrap is melted with the wrought iron, although such an addition 



ox the Strength of Materials 66 

does not improve the product. Since neither sulphur nor phosphorus are removed 
in this process only the purest stock can be employed. "The crucibles used in 
this country are made of graphite and clay and hold about ioo pounds of stock. 
Four to six of these covered crucibles are placed in a melting hole of a furnace 
and subjected to an intense heat. At the end of two or three hours the charge 
has become molten, but the crucibles are kept in the furnace ("killed") for another 
half hour so that silicon may be absorbed from the crucible by the metal and some 
of the gases boil out of the charge.* In the United States the furnaces are built 
on the regenerative principle and are heated by the combustion of hot gas and 
air. Such furnaces are provided with from two to twenty melting holes. In 
English practice the crucibles are placed in holes and surrounded by a coke fire. 

The Bessemer Processes. — The essential feature of the Bessemer process 
is the elimination of carbon and some of the other impurities by blowing a 
blast of cold air through molten pig iron. The blown metal is then converted 
into steel by adding a small amount of molten iron rich in manganese and carbon. 
This invention, so far reaching in its effects upon the manufacture and use of 
steel, is credited to the Englishman, Sir Henry Bessemer, and was patented by 
him in 1856. 

On account of radical differences in the amounts of certain impurities contained 
in the ores from various localities, two distinct divisions of this process have come 
into use, the acid Bessemer and the basic Bessemer processes. The adjectives 
acid and basic refer to the chemical characteristics of the linings of the con- 
verters in which the molten metal is blown. In the acid Bessemer process, 
which is the only one used in this country, the converter is lined with ganister, 
a silicious rock. Since this material has an acid reaction it will not be at- 
tacked by the acids formed in this process. In Germany, where the basic Bessemer 
process is extensively employed, the linings of the converters are made of a basic 
material, such as dolomite or magmesite, to resist the action of the basic slag 
produced in this process. 

Fig. 20 represents a 15-ton converter. As may be seen from the figure, a con- 
verter is a pear shaped vessel made of riveted steel plates lined with the refractory 
materials previously mentioned. It is mounted on trunnions so that it may be 
tilted to receive or pour the charge. Since the bottom of the converter wears 
out much more rapidly than the sides it is made detachable in order that it may 
be readily replaced by a new one. For the acid Bessemer process the average 
life of a converter bottom is about 30 or 35 heats. In fabrication, provision for 
admission of the blast is made by molding in the bottoms 18 or more vertical 
bricks. Each of these bricks is pierced by a dozen or more small holes, called 
tuyeres. When metal is being blown the air blast is forced through one of the 
trunnions, down the pipe fastened to the side of the converter, and up through 
the tuyeres into the charge. By making the air connection in this way it is always 
possible to tilt the converter without interfering with the blast. The pressure 
employed in the acid process is about 25 or 30 pounds per square Inch. 

Let us now follow the course of the metal from the blast furnace until east into 
an ingot. At the more modern plants of this country 150 to 000 tons of metal 
tapped from several blast furnaces is conveyed to a big steel-jacketed receiver 
or mixer which is lined with (ire brick. The receiver has a two fold purpose, to 
keep the metal hot and to provide a receptacle in which pig irons o\ different 

*These are the eomnioniy accepted theories but absolute knowledge concern- 
ing the react ions during " killing " is want ing. 



67 



Laboratory Notes 



analysis may be mixed to form a desired grade. Fig. 21 shows a vertical cross- 
section of a 300-ton mixer. At the older plants where the blast furnaces are 
situated at a considerable distance from the converters, or at plants where the 
analysis of the pig irons vary greatly, the charge from the blast furnace is cast 
into pigs. These pigs are classified by their fracture; the proper mixture is re- 
melted in a cupola and then carried to the converter plant. In many plants 





BOTTOM PLAN 



PLAN 




plates 




CROSS SECTION ELEVAT.ON 

FIG. 20. — A 15-TON BESSEMER CONVERTER. 



both cupolas and receivers are operated. Whatever the process may be, the pig 
iron is molten when conveyed to the converter. The latter is tilted to receive 
the charge from the buggy or ladle, and while it is being righted the blast is turned 
on. The oxygen in the blast immediately combines with and burns out the silicon 
in the bath, causing a considerable evolution of heat. The oxidation of manganese 



on the Strength of Materials 



68 



and some iron follows. These reactions produce an acid slag which floats on top 
of the metal . The temperature of the charge has now become so high that carbon 
is oxidized, causing a brilliant white flame to ascend 20 or 30 feet above the mouth 
of the converter. Ten minutes after turning on the blast the carbon flame 
drops, and the furnaceman knows that the carbon has been eliminated. The 
converter is now tilted, so that the metal lies in its belly, and a small buggy con- 
taining a predetermined amount of speigeleisen or ferromanganese is run forward 
and emptied into the bath. Both of these pig irons contain manganese, the 
former much more than the latter. Which one shall be used is determined by 
the carbon content desired in the steel. The addition of this recarburizer, as 
it is called, produces a boil in the metal; the manganese after withdrawing most 
of the oxygen passes into the slag while the carbon permeates the metal. It will 
be observed that no phosphorus or sulphur are gotten rid of in this process. The 
reason for this fact is that even though these elements become oxidized during 
the blow they are not soluble in an acid slag so they are immediately returned to 
the metal. Consequently, pig iron for use in the acid Bessemer process must 
have a low phosphorus and sulphur content. A fairly high silicon content is> 
however, desirable in order that the bath may be sufficiently heated to permit 
oxidation of the carbon. The charge is now poured from the converter into a 
ladle which serves the iron ingot molds. In filling the latter, metal is emitted 
through the bottom of the ladle so that the major portion of the slag may be pre- 
vented from passing into the ingot. When the molds are filled they are carried 
into the open air and stripped from ingots just as soon as the metal has cooled 
Commonly, an ingot is above 7 feet high, 14 inches square at the lower end and 
12 inches at the upper end. 




^jMLr-n-tedyML-JteB, 



FIG. 21. — A 300-TON MIXES 

In the basic Bessemer process metal is added with the molten pig iron to produce 

a basic slag. This slag will dissolve the silica which is formed and prevent the 



6 9 



Laboratory Notes 



latter from attacking the converter lining. The elements are oxidized in the 
same order as in the acid process until the carbon flame drops; then the phos- 
phorus, which runs high in basic Bessemer pig iron, is oxidized and dissolved by 
the basic slag with an evolution of much heat. If manganese is present in the 
bath some sulphur may also be eliminated in this process. Since it is difficult 
to determine by the appearance of the flame just when the phosphorus has been 
removed; a small sample is sometimes taken from the converter, cooled, and broken, 
in order that the amount of phosphorus remaining may be judged by the fracture. 
To avoid the returning of phosphorus from the slag to the bath, recarburizing 
cannot be done in the converter. Therefore, the slag is skimmed off as the metal 
is poured into a ladle before the recarburizer is added. The total time for a 
blow in this process is generally about 20 or 25 minutes. 

For the successful operation of the basic Bessemer process only pig irons which 
are high in phosphorus and low in silicon can be used. A low silicon content is 
desirable in order that the addition of lime and the consequent loss of heat may 
be as small as possible. A high phosphorus content is necessary so that the requi- 
site amount of heat may be produced to maintain a thickly fluid slag. If a con- 
siderable reduction in sulphur is desired the manganese content must also be high. 

The Open Hearth Processes. — The method of purification employed in the open 
hearth process consists in placing, a large quantity of pig iron and steel scrap or 
pig iron, scrap, and ore in a furnace equipped with a large shallow hearth and 
subjecting the charge to an intense heat generated immediately above the hearth 
by the combustion of hot gas and air This process, the most used of all, is the 
result of inventions of Sir W. Siemens of England, and Messrs. P. and E. Martin 
of France in 1861 and 1863, respectively. 

Two types of furnaces are used in this process, the stationary and the tilting 
furnace. The essential parts of either type are: a hearth lined with refractory 
material whose nature depends upon the character of the slag formed in the pro- 
cess; a covering for the hearth. so shaped that the temperature produced by the 
combustion of the entering gas and air will be deflected upon the hearth ; four or 
more systems of brick checkerwork — two for heating the gas and air while the 




FIG. 22. SECTIONAL ELEVATION OF STATIONARY OPEN HEARTH FURNACE, SHOWING 

CHECKER WORK HEARTH AND PORTS. 



on the Strength of Materials 70 

other two are being heated by the escaping gases; a series of passage ways and 
valves for controlling the admission of gas and air; a charging door in the front 
and a tap hole on the rear of the furnace. In Fig. 22 a vertical cross-section 
parallel to the front of the furnace indicates the arrangement and relation of the 
different portions of a stationary open hearth furnace. 

Open hearth furnaces are often called regenerative furnaces because the waste 
gases, which are at a much higher temperature than the entering gas and air, are 
utilized to reheat the cold checkworks. Producer gas is commonly used for fuel 
in this process. > This gas which is made by forcing a stream of air through a bed 
of red hot bituminous coal consists principally of nitrogen, carbonic oxide and 
hydrogen, with small percentages of carbon dioxide and hydrocarbons. 

At the large plants the open hearth furnaces are arranged end to end in a long 
row. One or more charging machines running on a track along the front of the 
furnaces serve to transport the pig iron and scrap from the stock piles to the fur- 
nace and charge the same. Ladles, carried by traveling cranes running along the 
rear of the furnaces, receive the molten metal from the tap holes and serve the 
ingot molds. To aid in forming a conception of the magnitude and arrangement 
of a 60-ton furnace and plant, Fig. 23 has been inserted. 

Just as in the Bessemer so in the open hearth process two divisions, acid and 
basic, are made. The hearth linings are made of the same materials as those 
employed in the Bessemer process. In the acid open hearth process the charge, 
consisting of about one-third pig iron and two-thirds steel scrap, is placed in the 
furnace and the gas and air turned on. The melter raises the temperature until 
the charge is melting at the desired rate. To determine the temperature of the 
bath he observes the rapidity with which a soft steel bar stuck into the bath 
will melt. Aided by such observations, he controls the temperature of the furnace 
by changing the time of reversal of the gas and air through the checkwork. At 
the end of about five or six hours the silicon and manganese have been practically 
burned out and the carbon content much reduced. The melter takes out a 
small ladleful of metal, pours a test piece, chills it in water, and from its fracture 
determines the carbon content. If he desires to burn out more carbon he adds ore 
to produce oxidation; if too much carbon has been burned out, he "pigs back,' 
or throws in pig iron to increase the carbon content. Tust before tapping, to 
remove oxygen from the metal and to stop further oxidation of the carbon, a 
small amount of ferromangane.se is thrown into the bath. Sometimes this so- 
called recarburizer is added in the ladle. Tapping is accomplished in the sta- 
tionary furnaces by unplugging the tap hole and allowing the metal to run out 
into a ladle or, in some cases, into a fore hearth in which it may be kepi hot for 
some time. The entire time for a heat runs 1 >ct ween six and ten hours. 

A rolling furnace is tapped by tilting it until tin- metal runs out of the tap 
hole which is always higher than the bath level when the furnace is in a horizontal 
position. This type of furnace can be tapped quicker and with more certainty 
than the stationary furnace since- delay due to plugging of the tap hole cannot 
occur, but it is rriore expensive in first cost and in upkeep. 

The common charge in the basic open hearth process is about equal amounts 
of steel scrap and pig iron (generally molten), a small amount of ore, and sufficient 
limestone to act as a (lux. Afh r three or four hours the charge has incited and 
most of the silicon, some manganese and some carbon removed. Phosphorus 
is now oxidized and absorbed by the slag; some manganese and sulphur combine 

Forming MnS which is dissolved in the basic slag. At regular intervals after the 
charge is melted the furnaceman casts a small test bar cools u m water, and breaks 



7i 



Laboratory Notes 




Q 

W 
H 
Ptf 
«! 
W 
M 

w 

Q 

fa 

O 

Oh 

<c 
w 

W 
O 



CO 



on the Strength of Materials 72 

it so that he may estimate the carbon and phosphorus content from the appearance 
of its fracture. Chemical analysis are also made during the heat. In making 
high carbon steel, it is good practice to reduce the carbon to 10 or 15 per cent, and 
then recarburize, since more gas and phosphorus are eliminated from the product 
by this procedure than by pouring when the carbon has been lowered to the de- 
sired percentage. On account of the basic slag the recarburizer must be added 
in the ladle for the same reason as given in the basic Bessemer process. The 
recarburizer generally consists of the ferromanganese and coke. This is broken 
up into small pieces and thrown into the ladle as the metal is poured. The time 
required to melt a heat by this process is slightly longer than that required for 
the acid open hearth process. 

It will be observed that neither phosphorus nor sulphur are eliminated in the 
acid open hearth process; consequently, only pig irons containing very small 
amounts of these elements can be used in this process. In the basic open hearth 
process, however, ores high in phosphorus and low in silicon are desired. 

The Use of the Electric Furnace in Steel Making. — Within the last five years 
rapid strides have been made in the use of the electric furnace both to refine and 
to produce steel. In 1909 there were 114 steel furnaces making steel ana seveu 
used in making pig iron. Some of these furnaces have been turning out 250 tons 
per day. At South Chicago one has been installed which has a capacity to refine 
500 tons of Bessemer steel in 24 hours. The electric furnace is similar to an open 
hearth furnace with electricity instead of gas and air as the source of heat. It 
has one great advantage over the other processes in heating the molten bath — 
no oxygen is required to supply this heat. 

The two types of furnaces most generally used are the electrode type and the 
induction type. In the electrode type of furnace the current enters through one 
electrode, passes through the bath, and leaves by the other electrode. In the 
Heroult furnace, one of the most extensively used types of furnace, the carbon 
electrodes both enter through the top of the furnace, see Fig. 24. According 
to Howe the electric furnace can desulphurize and deoxidize steel much more 
efficiently than any other process. It also can be used less efficiently to de- 
phosphorize steel. Consequently it is now being used to refine acid Bessemer 
steel made from ores high in sulphur and phosphorus. Crucible steel is being 
supplanted by steel made in the basic open hearth furnace and refined by the 
electric furnace. Excepting unusually favorable conditions, the high cost of 
electricity prohibits the commercial use of the electric furnace for the complete 
process of purification of steel. 

The Mechanical Treatment of Ingots. — Although some of the steel from the 
open hearth processes is made into steel castings, most of it together with Besse- 
mer steel is cast into ingots. The layman is apt to think of steel as a homo- 
geneous solid metal, but this conception is not generally correct. As an ingot 
solidifies three obstacles to a perfectly homogeneous structure are encountered : 
1. The metal on the outside cools before the metal on the inside so that, when 
the latter cools and shrinks, a cavity, called a pipe, is formed inside of the ingot 
near its upper end. 2. ( )bjeel ionable oxides of phosphorus, sulphides of iron and 
manganese, together with carbon segregate near the vertical axis o( the ingot 
toward its upper end. 3. Entrained gases and slag rise to the top of the bigot, 

forming blow holes. The first two difficulties can l»e almost wholly overcome by 
carefullj selecting the proportions of the differenl impurities; the only remedy for 

the last, however, is to cut off Hit top part or "crop" the ingot. The amount 



73 



Laboratory Notes 




'IG. 24. — TRANSVERSE SECTION OF A HEROULT ELECTRIC FURNACE. 
A, spout; E, electrode; H, roof; K, hearth lining. 



which should be cut off is often a bone of contention between the manufacturer 
and purchaser. 

It has been found that mechanically treating the ingot by forging, pressing, 
or rolling greatly improves the quality of the steel. Such treatment solidifies 
the metal, reduces the blowholes, and increases the cohesion and adhesion between 
the particles. The strength, specific gravity and hardness are consequently 
increased. The most pronounced effects of mechanical treatment are obtained 
when the work is carried on after the metal has cooled below a red heat. Under 
such treatment, the crystals cannot readjust themselves to the conditions which 
would naturally obtain if allowed to cool slowly from the higher temperature 
without mechanical treatment. By far the larger portion of structural shapes 
are made by reducing the ingot to the desired shape by passing it through a series 
of rolls. Before going to the rolling mill the ingot is first heated to a high welding 
temperature in a soaking pit or reheating furnace. After it has been passed through 
a couple of sets of rolls and its cross-section somewhat reduced it is cropped. It 
is next passed on through a series of 10 or 15 rolls, the number depending upon 
the shape and size of the desired piece, sawn to the desired length and slid off 
to one side to cool before being transferred to the stock pile. Fig. 25 shows an 
elevation of a set of I-beam rolls. Fig. 26 represents a double stand of rolls 
used in a plate mill. The forms commonly rolled are blooms, slabs, plate?, rails, 



on the Strength of Materials 



74 



rods, merchant bars, and all kinds of structural shapes, such as I-beams, angles, 
tie bars, etc. 




FIG. 25. — THREE-HIGH LIGHT I-BEAM ROLLS. 




FIG. 26. — THREE-HIGH PLATE MILL, TWO-HIGH STRANDS OF ROLLS. * 

B, COUPLING BOXES; D, SCREW DOWN MECHANISM; E, ROLL ENGINE; H, HOUSING; P, PINIONS; 

PH, PINION HOUSING; RR, ROLLS; S, SPINDLES. 

Comparison of Steels Made by Different Processes. — The crucible process is 
much more costly than the Bessemer or open hearth processes,; bur, 0:1 account 
of being under better control, this process furnishes a more uniform and much 
better grade of steel for the manufacture of tools, cutlery, springs, projectiles, 
etc. It is claimed that just as high grade steel can be produced by the electric 
furnace as by the crucible process and at less cost. (Engr. News, Page 637, 
Vol. 61). By far the largest amount of steel is made into structural elements, 
railroad rails, plates, sheets, merchant bars, wire, rods, etc. For such grades of 
material the acid open hearth process makes the most economical steel. It is 
considered better than the basic open hearth because it may be recarburized in 
the furnace. In the basic process there is danger of some basic slag being carried 
into the ladle, a condition which produces rephosphorization. Furthermore, 
this basic slag may withdraw some of the silicon from the bath, thus producing 
a metal which will be low in silicon and which will not make sound ingots. Bv 



St mtfhton's Metallurgy of Iron and S(c,l. 
Hook Co. 



Second Edition, copyritfhl 1911 by McGraw-Hill 



75 Laboratory Notes 

recarburizing in the furnace a more uniform distribution of the effects of the recar- 
braizer are obtained. However, owing to the high cost of ores low in phosphorus 
and sulphur, there is a tendency in the acid processes to use ores which are too 

high in these mcpmukies, a danger mouth should mc he overlmlmd in estimating 
the relative value of the processes. Again, the hasi: m en hearth ::: cess is super- 
cr to the acid Bessemer process teeau.se it is a longer prceess under ninth tetter 
centre!. There is much mere oxygen present in Bessemer metal than in the c re- 
luct :t the casic men hearth furnace. Furthermore, since ah :t the carton is 
turned cut in the Bessemer prceess cefere re cart uniting , the carton : intent of 
high lam :n sreel carmzt he very accurately predetermined. On the ctner hind. 
in steels made hy the casic t pen hearth rurrate the uliimate lam m cement :ar 
be more closely predetermined, sin:e only a portion of tie required carbon is 
added in toe recamuriier. hue extreme meanness :f the Bessemer pro cess has 
given it a great advantage in certain lines ;f manufacture, such as the rail, steel 
pipe, and wire industries. Nevertheless, no tetter evidence of the growing 
popularity of the h a s i : men hearth pre cess need ce given than the triduetizn 
statistics. In mist large .American steel mams it has teen fiund advantageous 
to employ both the acid Bessemer and the basic open hearth processes. In 
this way the ultilization of all grades of pig iron is made possible. 

In conclusion we may say that in quality of product the different processes 
rank as follows: I, crucible and electrically refined steel; 2, acid open hearth; 
3, basic open hearth; 4, acid Bessemer. In cost the crucible process also leads 
with the electrically refined steel second and the remainder in the above named 
order. 

XL LIMES AND CEMENTS 

Introduction. — In trier :: liind tigether the inert particles cempesing a f turd- 
use four materials: I, lime in variius forms: 2, natural cement: 5, ? Ireland 
lentent: t. asphalt. Only the first three 11 these mill ce cinsidered herein. Tim 
methe Is if metaratim and uses if asohalt mav lie found in anv standard : 1: 



I. LIMES. 

Lime. — Pare lime, generally called quick lime, is a white oxide of calcium or 
a combination of the oxides of calcium and magnesia. Its specific gravity is about 
j. 10. Essentially, the process of making lime consists in heating either pure or 
1 a gn e s mm limes 1 1 : _ e ha h 1 : : : C a C 3 — Mg C0 3 ) to a temperature sufficientiy 
high to break up the carbonates into oxides of lime and magnesia (Ca O — Mg O) 
and carbon dioxide (CO*). For pure lime carbonate, the temperature at which 
sum disss elation takes olace is all 1 ut io: : I 

Limestone is usually burnt in some form of vertical kiln. The raw material 
is fed in at the top and the finished product drawn off at the bottom. In general 
the stacks of these kiln*; consist of cylindrical steel shells lined with refractory 
brick. Kilns may be operated continuously or intermittently. To secure the 
greatest efficiency continuous operation is imperative. The common types of 
kiln are the "mixed feed" and separate feed kilns. In the mixed feed type; 
bituminous coal and limestone are mixed together and fed into the top of kiln, 
in the separate feed type, the limestone is not brought into contact with the fuel 



on the Strength of Materials 



76 



during the burning process. To accomplish this, the fuel is burned in a grate 
which is attached to the sides of the kiln (see Fig. 27) and so arranged that the 
heat produced will ascend into the stack. The mixed feed kiln is more economical 
of fuel but docs not produce as high grade product as the separate feed kiln. 




FIG. 27. — SEPARATE FEED LIME KILN. 

In Germany kilns of the ring type are much used. These consist of horizontal 
chambers arranged in a circular or elliptical ring which arc connected to a cen- 
tral stack. Each chamber is connected to its neighbor and to the stack by separate 
flues. The limestone and fuel are fed into the chambers from the top and a 
fire started in one of the compartments. The flues in all the chambers are then 
arranged so that the hot gases from the burning compartment must pass around 
the ring through all the other chambers before going to the chimney. This pro- 
cess is very economical in utilization of the heat in the fuel and has been used 
abroad both in the manufacture of brick and Portland cement. 

Lime is made in nearly every state and territory in the United States. The 
leaders in production are: (1) Pennsylvania, (2) Ohio, (3) Maine, (4) New York. 
The total output of the U. S. in 1910 was 3, 481, 780 short tons, valued at $13, 894, 
962. 

Hydrated Lime. — If 18 parts of water be added to 56 parts ofpurequiek lime 
the mixture swells with an evolution of considerable heat and increases in volume 
about 300 percent. The final product is a fine white powder having a specific 
gravity of about 2.08. This process is called slaking and the product is named 
hydrated line (CaOIL). 

Since quicklime, if exposed to the atmosphere, will absorb more or less 



77 Laboratory Notes 

moisture and become partically slaked; it cannot be stored for any length 
of time in the lump form. In construction it is usually mixed with a 
considerable excess of water, thereby weakening the strength of the paste, and 
kept under water until used. Furthermore, owing to variations in the amount 
of impurities present in lump lime, the quantity of water and the length of time 
required for slaking will vary. Limes high in magnesia (poor limes) will require 
less water and slake more slowly than high calcium limes (fat limes). Therefore, 
the slaking of lump lime can be much more efficiently done in a specially equipped 
plant than on the job. On this account, a considerable demand has arisen for 
hyd rated lime. 

Commercial hydrated lime, or limoid, is prepared by finely grinding lump 
lime, thoroughly mixing it w T ith sufficient water to produce complete hydration, 
and screening through a sieve having 50 meshes per linear inch. The product is 
then packed in 100-lb. bags for shipment. 

Properties and Uses of Lime. — On account of the excessive amount of shrinkage 
which takes place in the hardening of neat lime paste it is always necessary to 
mix sand with the paste to lessen the tendency to crack. Usually the proportion 
is one part lime to two parts sand. 

In hardening, the mortar dries out and absorbs carbon dioxide from the air 
forming calcium carbonate. Unless there is a free circulation of air into all 
parts of the mortar this hardening action cannot take place. Therefore, it is 
only at the exposed surfaces of the joints that lime mortar becomes completely 
hardened. 

The tensile strength of 1 :2 lime mortar two months old may be taken at 30 lb. 
per sq. in. The high magnesian limes are weaker in strength during the early 
age of the specimens but at an age of six months become stronger than specimens 
made from high calcium lime. At an age of one year 1 :2 mortar specimens 
made of high magnesian limes show a strength of 80 to 90 lb. per sq. in.* 

In construction work slaked lime is chiefly used to make mortar for laying 
brick and stone masonry and for plastering buildings. It should only be used 
in joints or places exposed to the atmosphere. 

Hydraulic Lime. — In the middle of the eighteenth century John Smeaton, 
the celebrated English Engineer, was confronted with the problem of finding a 
cement which could be used in the construction of the famous Eddy stone Light- 
house. The only cementing material then in use was quicklime, which does not 
harden under water. After a series of experiments he discovered that an impure 
limestone containing a small amount of clay, if calcined in the ordinary way, 
would produce a lime which would slake upon the addition of water and would 
harden under water. On account of the latter property the name hydraulic 
lime w T as given to this material. In France and southern Europe it is still used 
to a considerable extent. On account of the prevalence of raw materials suit- 
able for the manufacture of Portland and Natural cements no hydraulic lime is 
manufactured in the L T . S. However, Lafarge cement, a by-product in the manu- 
facture of hydraulic lime, is used considerably in this country. 

Hydraulic lime is manufactured in the same way as quick lime, although a 
somewhat higher temperature is required in burning. In slaking, considerable 
care is required to provide just sufficient water and no excess, since an excess 



*For further data on tensile strength see Report of the Chief Engineers, 
U. S. A. for 1896 part 5, P. 283-5 Municipal Engineering, Vol. 28 P. 47, 
Jan. 1905. Engineering News, Vol. 51, P. 543 — June 9, 1904. 



on the Strength of Materials 78 

would cause the lime to harden. After slaking, the coarse material is screened out 
and the fine product bagged for market. The coarse particles are finely ground and 
sold for Natural cement. The specific gravity of hydraulic lime is about the same 
as that of the Natural cement. Mortars made from the famous limes of Tiel, 
France, also have about the same strength as those made from Natural cement. 

2. NATURAL CEMENT 

Definition. — Natural cement is made by burning a natural argillaceous lime- 
stone at a low red heat (1000 to 1300° C), which is sufficient to drive off car- 
bonic oxide (CO,). The clinker will not slake to any extent and must be finely 
ground before it exhibits hydraulic properties. 

Process of Manufacture. — The argillaceous limestone is burnt in vertical kilns 
30 to 40 ft. high and 10 to 15 ft. in diameter. The common type of kiln consists 
of a cylindrical steel shell open at the top and lined with fire brick. In operating 
a kiln thick layers of limestone and thin layers of soft coal are alternately dumped 
into the top of the kiln and the burnt clinker is drawn off at frequent intervals 
from the bottom. As the limestone descends in the kiln, water is first driven off 
from the rock. At a temperature of about 700 C. magnesian carbonate 
begins to decompose. Lime carbonate dissociates at 8oo° C. and clay 
at a somewhat higher temperature. The alumina and iron oxide set free by the 
decomposition of the clay combine with the lime and magnesia and if the final 
temperature be high enough lime and magnesian silicates will be formed. The 
process is run continuously and about one- third of the charge, in the form of 
clinker, is daily withdrawn from the kiln. 

At the Milwaukee Natural cement plant, the kiln capacity is about 400. bbl. 
of cement of 265 lb. each, or 130 bbl. per day. The amount of soft coal consumed 
at this plant averages about 30 lb. per bbl. of cement. 

On account of the variations in the quality of the raw material and non-uni- 
formity in burning different parts of the charge, a considerable portion of the 
resultant clinker is either under burned or over-burned. According to Eckel 
from 10 to 33 per cent, of the resultant product cannot be used. After the clinker 
has been removed from the kiln it is allowed to season in the air in order that any 
under-burned clinker may be slaked before grinding. Sometimes slaking is ac- 
celerated by steaming the clinker. 

The burnt clinker is first passed through a stone crusher and then fed to some 
form of apparatus for grinding it to the requisite fineness. Formerly, all mills 
used the millstone grinders commonly employed in flour mills. More recently, 
however, a decided improvement in the fineness of grinding has been affected by 
the introduction of ball mills, tube mills and other modern equipment used in 
grinding Portland cement. 

Natural cement has been extensively used in sewer work, masonry construction, 
and in monolithic or massive construction in concrete in which great strength 
was not required. Since the year [899, however, the production of Natural 
cement in the U. S. has steadily declined. This decline has been brought about 
by the decrease in the cost of Portland cement, lu 1 <) 1 <> the production of Nat- 
ural cement was [,139,239 bbl. valued at 43.3 cents per bbl. 

Characteristics of Natural Cement. Natural cement is an impalpable powder 
varying in color from yellow to brown and in specific gravity from 2.80 to 3.00. 
It resembles hydraulic lime inasmuch as it is made from a natural argillaceous 
limestone and will sel when mixed with water either in air or under water, ( hi 



79 



Laboratory Xotes 



the other hand, natural cement clinker slakes but little, if any, when water is 
poured upon it. 

The chemical composition of natural cement is decidedly variable. It is made 
from a limestone containing from iotozjX) percent, of clay without any adultera- 
tion. The approximate limiting proportions of the chief chemical compounds 
found in natural cements, as obtained from over ioo analyses found in Eckel's 
Cements, Limes and Plasters ch. XIX, is as follows: — 30 to 60 per cent, of 
lime (CaO); 15 to 35 percent, of silica (Si0 2 ); 1 to 25 per cent, of magnesia (MgO) ; 
2 to 20 per cent, of alumina; 1 to 19 percent, of iron oxide; and, in general, less than 
10 per cent, of water, carbon dioxide, the alkalies (K 2 0, Na 2 0), and sulphur 
trioxide (S0 3 ). 

On account of the differences in the degree of calcination and the wide varia- 
tion in chemical composition, the properties of natural cements often differ 
considerably. 

Tests of Natural Cement. — The standard specifications for natural cement 
prepared by the A. S. T. M. give the standard tests and results which should 
be gotten from tests on such cements. Fig. 28 shows the average strength- 
time curves for a number of representative natural cements. 



500 




1 7 S8 

K-Days-H<— 



FIC. 28. TENSILE STRENGTH OF NATURAL CEMENT. 

(From Taylor's Practical Cement Testing) 

In compression neat natural cement cubes 28 days old, should average 800 
and those made of 1 :2 sand mortar 500 lb. per sq. in. The consistency of the 
mixture bears an important relation to the strength; consequently, the standard 
consistency should be used in making test specimens if results for purposes of 
comparison are desired. Allowing the cement to aerate increases, to some extent, 
the time of set and decreases the strength. Natural cement, therefore, should 
not be stored exposed to the air for more than two weeks. The resistance of 
natural cement to low temperatures is small; consequently, it is net advisable 
to use it in work which is liable to be exposed to frost before the concrete is dry* 
The use of salt in the mixing water to lower the freezing point is to be condemned, 
since it greatly decreases the strength of natural cement mortars. 

3. PORTLAND CEMENT. 

Growth and Importance of the Portland Cement Industry. — On account of 
the superior properties possessed by Portland cement, the widely distributed 
sources of the raw materials from which it is made, its cheapness, and the decline 
in the supply of timber, the Portland cement industry has had a marvelously 
rapid growth. Although the process of manufacture of this material was dis- 
covered by Joseph Asdin of Leeds, England, in 1824; it was not intil 1859 that 
any considerable quantity was used in England, and not until 1875 that any 



on the Strength of Materials 80 

progress was made in the manufacture of this cement in the United States. Dur- 
ing the latter year, the pioneer Portland cement plant in the United States was 
started by Messrs. D. O. Saylor, E. Rehrig and A. Woolever at Coplay, Pa. The 
plant bearing Saylor's name is still running to-day with a very much increased 
capacity. An estimate of the rapidity of growth of this industry may be formed 
by comparing the quantity produced in 1880 — 42,000 bbl. — with the output 
for the United States in 191 1 — 78,528,637 bbl. The value per barrel at mill 
in 1880 was $3, in 191 1 it was 84.4. cents. 

Definition. — A properly proportioned mixture of argillaceous and calcareous 
materials which has been finely ground, calcined to incipient fusion, reground 
to an impalpable powder, and to which no addition of over 3 per cent, has been 
made subsequent to calcination, is called Portland cement. 

Raw Materials. — Arranged in the order of importance, the raw materials most 
commonly used in the manufacture of Portland cement and the parts of the United 
States in which they are employed are : 

Materials Where used in making Portland Cement 

Calcareous Argillaceous 

Limestone Shale or clay Widely used, Eastern N. Y., Mich., 111., Ind. 

Limestone Cement rock Eastern Penn. and N. J. 

Limestone Blast furnace slag Illinois, Ohio, Penn. 

Marl Shale or clay Central N. Y., Ohio, Mich., Ind. 

Cement rock is a soft impure limestone containing 20 per cent, or more of clay. 

Marl is a soft calcareous deposit found in the bottoms of shallow lakes, swamps 
or in old fresh water basins. 

Shale contains practically the same proportions of alumina (ALO :i ) and silica 
(Si0 3 ) but less water than clay. A common form of shale is slate. 

In order that the proper chemical combinations may obtain in the kiln, all 
calcareous materials must be free from quartz or sand and contain but little 
sulphur or magnesium carbonate. According to Edwin C. Eckel,* phosphorous 
pentoxide, P a 5 , is another undesirable element. Soft limestones are preferable 
to hard ones of the same chemical composition since they can be more easily 
crushed and ground. Clays for this process should also be free from sand — that 
is, the silica should be chemically combined with the alumina in the form of 
kaolin (ALO :1 , 2 Si 2> 2 H 2 0). With reference to the proportions of the main 
constituents R. K. Meade states that the ratio of the silica to the alumina con- 
tent should be between 2.5 and 4 to 1 and that there should not be more iron 
oxide than alumina.t 

The first step in the manufacture of Portland cement is the winning of the raw 
materials from nature. The hard raw materials are blasted, loaded onto small 
cars, and drawn to the cement mill. Soft materials like clay or marl are dug or 
excavated with a steam shovel or dredge, depending on the nature of the deposit. 

The Dry Process of Manufacture. — In general, only the comparatively dry 
raw materials, such as limestone and cement rock, limestone and shale or clay, 
and limestone and blast furnace slag, are used in the dry process of manufacture 
of Portland cement. The steps in the process of manufacture are: 1, crushing 
of raw materials; 2, drying; 3, grinding; 4, proportioning; 5, final pulverizing of 

*Cements, Limes, and Plasters, by E. C. Eckel, p. 389. 

1[ Portland Cement, by R K. Meade, p. 54. 



8 1 Laboratory Notes 

raw materials; 6, burning; 7, cooling the clinker; 8, adulteration to retard set; 
9, reduction of clinker to an impalpable powder; 10, seasoning of cement; 11, 
bagging. The order of the first four of these operations varies at different plants 
and it is dependent to some extent upon the character of the raw materials. 

Crushing of the hard materials is largely done in gyratory crushers, although 
a few plants pass material from the quarry through toothed rolls. Generally, 
the material must be passed through a large and a small crusher in order that the 
requisite fineness for successful operation of the grinding mills may result. 

Since it is necessary to have the raw materials in an approximately dry state 
before grinding, most of these materials must be passed through some sort of a 
drying apparatus. In most plants a dryer consists of hollow steel cylinder about 
50 ft. long and 5 ft. in diameter, revolving about its geometrical axis which is 
inclined at a small angle with the horizontal. The raw materials enter at the 
upper end and pass out at the lower end of the cylinder. The source of heat, 
which is commonly an attached furnace or waste gas from the rotary kilns, enters 
?t the lower end and passes out at the upper. To increase the circulation of the 
materials through the hot gases, lugs which serve to elevate and scatter the 
charge, are rivetted on the insiae of the dryer. 

Preliminary grinding is quite extensively carried on in a ball mill or in an 
improved type of ball mill called a kominuter. Fig. 29 shows a common 
type of ball mill. As may be seen in the figure, the entire machine is en- 
closed by a stationary steel casing to prevent the escape of the dust which 
arises during the grinding process. To permit rotation of the machine, the 
drum heads at each end of the mill are equipped with trunnions. Through 
a hole in one of these trunnions, the material to be ground is fed into the 




FIG. 29. — BALL MILL. 



mill. For the purpose of pulverizing, about two tons of hard steel balls, varying 
from three to five inches in diameter, are ordinarily employed. The interior 
of the mill is provided with three cylindrical linings of which the innermost con- 



Laboratory Notes 



82 



sists of a set of overlapping steel plates, called wearing plates. The latter receive 
the abrasion and impact produced in grinding. Between the plates openings are 
provided through which the fine material passes onto the second lining, a coarse 
screen. Further sifting of the material passing the coarse screen is performed by 
a fine seive which surrounds the coarse one. During a revolution the residues 
from both sieves drop back into the mill and are reground; the fine material 
leaves the machine through a chute in the bottom of the casing. A large ball 
mill of this type will reduce to a No. 20-mesh four or five tons of material per 
hour. 

The finishing stage in the grinding process is performed at many plants in a 
tube mill. This mill is also steel jacketed, cylindrical in shape and revolved about 
its geometrical axis. Commonly, such a mill is about 22 ft. long and 5 or 6 ft. 
in diameter. In order to form a surface with a high resistance to abrasion, the 
inside of the drum is lined either with trap rock, silex, or chilled cast iron. 




FIG. 30. GATES TUBE MILL. 

The pulverizing is accomplished by flint stones about the size of goose eggs, 
which fill the inside of the mill about half full. Recently, increased efficiency in 
operation has been attained by the replacement of a portion of the flint stones 
by small metal slugs called "cylpebs." 

Fig. 30 shows a side view of a tube mill. From this figure it will be noted that 
the heads support hollow trunnions whose axes coincide with the geometrical 
axis of the cylinder about which the mill revolves. A screw conveyor at the 
driving end of the tube mill serves to force the material through the opening in 
one of the trunnions. The material leaves the mill through the trunnion at the 
opposite end or through a circumferential screen placed near it. In grinding 
raw materials the average tube mill will turn out 4 or 5 tons per hour or it will 
reduce 10 or [8 bbl. of clinker to cemenl in the same time. 

Fig. 31 shows a sect ional elevation of a Griffin mill which is used in many plants 
as a substitute for the tube mill. In this machine the materia] enters the pan at 
the bottom and is forced upward between the circular die and revolving ring. 
The latter is rotated at approximately [50 r. p. m. by means of the pulley and 

universal joint at the top of the shaft SO th.it. there is developed between the die 



83 



Laboratory Notes 



and ring a very large centrifugal force which rapidly pulverizes the material. 
A current of air carries the fine material upward through screens in the top of 
the pan while the coarse material falls to the bottom and is reground. 




THE GIANT GRIFFIN MILL 
FIG. 31 SECTIONAL ELEVATION OF A GRIFFIN MILL. 

Another type of grinding mill often used on raw material is the Lehigh-Fuller 
shown in Fig. 32. In this mill four 12-inch steel balls are pushed around an 
annular die by means of horizontal radial arms set 90 degrees apart on the 
vertical shaft. Since the shaft runs at 160 r. p. m. the balls exert a large force 
against the die. The materials are fed to the mill from a hopper on top, 
which is provided with a feeder operated from the mill shaft. The material 
is discharged by the feeder between the balls and the die and is thus reduced 
to an impalpable powder. By means of a fan. arranged on the arms pushing 
the balls, the powdered material is blown into a compartment just above the 
zone of pulverization whence another fan forces it through a set of fine screens 
and discharges it from the machine. 

There are several other types of grinding machines, the Maxecon, Huntington 
Raymond, Sturtevant Ring-Roll mill, etc., but lack of space prohibits a further 
discussion of them. 

After the raw materials have been proportioned, intimately mixed, and very 
finely ground, the powdered product is conveyed to kilns to be birncd. Formerly 
the vertical intermittent type of kiln, somewhat like that used in the production 
of natural cement, was employed to burn Portland cement. In Europe use is 
still made of this type, and in Germany the Hoffman ring kiln, briefly mentioned 
in the manufacture of natural cement, is quite extensively employed. However, 



on the Strength of Materials 



84 




TIG. 32. — LEKIGII-F1 i.l EJR MILL. 



in the United Stales the continuously operated rotary kiln is favored to the ex- 
clusion of all others. 

From Fig. 33 one can obtain a notion of the appearance of a rotary kiln. It 
consists of a cylindrical jacket made of riveted ste si plates lined with refractory 
fire bricks. The lower end of the kiln is covered by a detachable hood provided 
with two openings. Through one of these openings is passed a nozzle for the ad- 
mission of fuel. The fuel most commonly employed is powdered coal. In order 
to introduce the coal into the kiln and to secure both rapid and complete com- 
bustion, it must be so finely pulverized that 95 per cent, will pass a No. 100 sieve. 
The coal is blown through the nozzle by an air blast. The second opening in 
the hood is provided to enable the operator to observe the interior ol the kiln 

during calcination. The steel jacket is surrou ided by two or more heavy steel 
tires, by means of which it is. rotated on friction roller bearings. These bearings 
are so adjusted that, the axis of the kiln has an inclination with the horizontal 



Laboratory Notes 




FIG. 33. — ROTARY KILN. 

of Y*, inch per foot. By thus inclining the axis, the material is slowly moved 
downward from the upper end as the kiln is rotated. Rotation is produced 
by a motor placed near the center and geared to a girth gear attached 
to the jacket. The upper end of the kiln enters a brick flue from which the pro- 
ducts of combustion escape to the stack. Passing through this flue is an inclined 
spout which discharges the finely powdered raw material into the kiln. 

Soon after the entrance of the material it begins to ball up into small marble- 
like shapes. During the first half of the passage toward the hood any entrained 
water is evaporated and the material is heated to a temperature sufficient to expell 
carbon dioxide (C0 2 ) from the limestone. By the time the clinker has reached 
within a few feet of the lower end of the kiln its temperature has risen to 1600 
to 1700 C, and all carbon dioxide, sulphur, and organic matter have been 
expelled. The little soft yellowish brown balls have now partially fused into 
hard greenish black clinker.* At many plants the degree of calcination is left 
to the skill of the burner, who regulates the speed of rotation of the kiln so that 
the clinkering zone is kept back a few feet from the discharge end. He is able 
to judge of the position of this zone by the greenish flame which is emitted when 
the material begins to burn and form clinker. Under ordinary conditions a 
speed of 30 or 40 revolutions per hour secures the requisite degree of calcination. 
At the end of 4 or 5 hours the burning process is completed and the clinker falls 
out of the kiln through a trap in the lower side of the hood, whence it is conveyed 
to the cooler. The clinker is quite irregular in shape and varies from the size 
of a walnut down to a buck shot. It is very hard, has a more or less vitreous 
luster, and is generally black or greenish black in color. 

Most modern kilns are from 100 to 1 50 feet long and fom 6 to 9 feet in diameter. 
At present the tendency is toward the use of longer kilns. The capacity of kilns 
of the sizes mentioned will vary from 400 to 800 barrels per day. In producing 
a 376-pound barrel of Portland cement, from 600 to 700 pounds of raw material 
and 30 to 120 pounds of coal is consumed. 

To facilitate grinding, the clinker is now cooled by spraying with a water jet 
and passing through a cooler. Frequently the cooler consists of a vertical or 
horizontal steal cylinder equipped with devices for agitating the material. As 
the clinker passes through the cooler it meets a forced air draft, which rapidly 



*For further information concerning the chemical changes in a 
see R. S. Meade's Portland Cement, pp. 176 to 199. 



rotary kiln, 



on the Strength of Materials 86 

lowers its temperature. At some plants the clinker is cooled out of doors. After 
cooling, about 2 per cent, of gypsum is added to lessen the time of set of the result- 
ing cement. At many plants the adulteration is done after the clinker has been 
through the ball mill. In grinding the clinker, the same kind of machinery is 
generally used as is employed in pulverizing the raw materials. Whatever 
grinding machinery is used, the resultant fineness must be such that 92 per cent, 
of the cement will pass a sieve with 100 meshes per linear inch and 75 per cent, 
will pass one with 200 meshes per lineal inch.* On account of the fact that a 
finely ground cement will make a stronger mortar than a coarsely ground one, 
many plants endeavor to secure a degree of fineness, considerably in excess of the 
above figures. At present, however, the economical limit to which fine grinding 
may be carried seems to be about 85 per cent, through a No. 200 sieve. 

From the grinding mills a conveyor carries the cement to the storage bins, in 
which it is generally kept for a few weeks before being bagged for shipment. This 
seasoning period seems to improve the quality of the cement. In support of 
this statement, it seems quite possible that unburnt lime might be sealed within 
the clinker during the burning period and be liberated during the grinding process. 
Upon exposure to the air such particles of lime would absorb carbon dioxide 
(C0 2 ), and become calcium carbonate (Ca C0 3 .) This substance is not affected 
by the addition of water, is inert during the setting of the cement, and therefore 
does no harm. 

In accordance with the demand of the trade the cement is conveyed from the 
storage bins to the packing house. Here it is automatically weighed and packed 
by machines sometimes in wooden barrels containing 376 lb., net, but more 
frequently in cloth sacks which hold 94 lb., net. The cement is now ready for 
shipment. 

In order that an idea of the arrangement of a cement mill may be gotten, Fig. 
34, showing a plan and vertical section of the Hudson Portland Cement Company's 
plant has been inserted. 

The Wet Process of Manufacture. — 'By far the larger portion of the cement 
manufactured in the United States is made by the dry process. Under favorable 
conditions, however, the wet process is successfully and economically employed. 

The raw materials most commonly used in the wet process are marl and clay. 
Preparatory to mixing the materials, the marl is often screened and pumped, in 
the form of thin mud, from the deposit directly into large storage basins situated 
near the kilns. The clay is dried, for convenience in calculating the mixtures, 
and pulverized in an edge runner or similar mill, Fig. 35. Then, proper quantities 
of the two materials determined by a chemical analysis are weighed out and mixed 
by passing through a pug mill. This wet mixture, or slurry, from the pug mill 
consists of about two-thirds water and one-third marl and clay. The slurry 
is next pumped into large vats, in which it is continually agitated to maintain the 
uniformity of the solution. From these vats samples are taken for analysis; 
and, if necessary, additions of marl or clay are made until the desired composition 
is obtained. The slurry is now pumped into especially constructed rotary kilns 
and burned. The succeeding stages in the wet process of manufacture arc similar 
to those described under the dry process. 

Comparison of Wet and Dry Processes. — The chief advantage possessed by 
the wet process is the well regulated control which is obtained over the raw mix- 
ture. On the other hand, the wet process requires about one-third more fuel 
per barrel of cement than the dry process and (lie kiln capacity is about 2^ per cent. 
less than in the dry process. Although this increase in the cost of production 
by the wet, process is partially offset by the higher cost of grinding the raw ma- 
terials in the dry process, yet it is only when the raw materials ran be gotten under 
very favorable conditions that a wet process cement can be made at a price which 
can compete with a cemenl made by the dry process. 



See standard cemenl Specifications of the A. S. T. M. 



S7 



Laboratory Xotes 




in 



ON 



the Strength of Materials 




FIG. 35- DRY PAN 



!7;2 



89 



Laboratory Notes 



XII. CONSTANTS OF STRENGTH FOR STRUCTURAL 

MATERIALS 

Fairly Representative Values for Use in Classes in Mechanics 
Elastic Limits, Tension and Compression 



Wrought Iron 



Structural and Machinery Steel 4 o 

Ultimate Tensile Strengths 



30 000 lb. per sq. in. 
000 " " " 



Timber 

Cast Iron 

Wrought Iron '..'.'.'... 

Structural and Machinery Steel 60 000 



10 000 lb. per sq. in. 
30 000 " " " 



Ultimate Compressive Strengths 

Brick 

Brick walls in mortar 

Rich Concrete, one month old or over • 

Stone 

Timber 

Cast Iron 



3 000 lb. per sq. in 

75° 

2 000 " 
6 000 " " 

8 000 " 
90 000 " " 



Ultimate Shearing Strengths 



Brick 

Stone 

Timber, with grain - 00 

Timber, across grain 3 000 

Cast Iron 18 000 

Wrought Iron 40 000 

vStructural and Machinery Steel '. . 50 000 

Computed Flexural Strengths [Moduli of Rupture] 

Brick 800 lb. 

Stone 

Timber 

Cast Iron 



1 000 lb. per sq. in 
1 500 





800 It 


). per 


sq. in. 


2 


000 " 




if (i 


9 


000 " 




(i «i 


35 


000 " 




<( << 



Moduli of Elasticity in 

Tension or Compression 

(lb per. sq. in.) 

Brick 2 000 000 

Stone 6 000 000 

Timber 1 500 000 

Cast Iron 15 000 000 

Wrought Iron 25 000 000 

Steel 30 000 000 



Factors of Safety for Steady Loads 

Timber 6 

Cast Iron 6 

Wrought Iron 4 

Steel 4 

Stone and Brick 15 

Concrete 5 



V 73 






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